diff --git a/girepository/compiler/meson.build b/girepository/compiler/meson.build
index f724f32c5..eb704761e 100644
--- a/girepository/compiler/meson.build
+++ b/girepository/compiler/meson.build
@@ -3,6 +3,7 @@
 
 custom_c_args = [
   '-DG_LOG_DOMAIN="GLib-GirCompiler"',  
+  warning_sign_conversion_args,
 ]
 
 if cc.get_id() != 'msvc'
diff --git a/girepository/decompiler/meson.build b/girepository/decompiler/meson.build
index cb4553262..b6090f61f 100644
--- a/girepository/decompiler/meson.build
+++ b/girepository/decompiler/meson.build
@@ -3,6 +3,7 @@
 
 custom_c_args = [
   '-DG_LOG_DOMAIN="GLib-GirDecompiler"',
+  warning_sign_conversion_args,
 ]
 
 if cc.get_id() != 'msvc'
diff --git a/girepository/giarginfo.c b/girepository/giarginfo.c
index 8728fd0d6..5d048377e 100644
--- a/girepository/giarginfo.c
+++ b/girepository/giarginfo.c
@@ -286,7 +286,7 @@ gi_arg_info_get_closure_index (GIArgInfo    *info,
   has_closure_index = (blob->closure >= 0);
 
   if (out_closure_index != NULL)
-    *out_closure_index = has_closure_index ? blob->closure : 0;
+    *out_closure_index = has_closure_index ? (unsigned int) blob->closure : 0;
   return has_closure_index;
 }
 
@@ -317,7 +317,7 @@ gi_arg_info_get_destroy_index (GIArgInfo    *info,
   has_destroy_index = (blob->destroy >= 0);
 
   if (out_destroy_index != NULL)
-    *out_destroy_index = has_destroy_index ? blob->destroy : 0;
+    *out_destroy_index = has_destroy_index ? (unsigned int) blob->destroy : 0;
   return has_destroy_index;
 }
 
diff --git a/girepository/gicallableinfo.c b/girepository/gicallableinfo.c
index 551fe961d..48b1fc679 100644
--- a/girepository/gicallableinfo.c
+++ b/girepository/gicallableinfo.c
@@ -80,7 +80,7 @@ signature_offset (GICallableInfo *info)
       g_assert_not_reached ();
     }
   if (sigoff >= 0)
-    return *(uint32_t *)&rinfo->typelib->data[rinfo->offset + sigoff];
+    return *(uint32_t *)&rinfo->typelib->data[rinfo->offset + (unsigned) sigoff];
   return 0;
 }
 
@@ -354,8 +354,8 @@ gi_callable_info_get_n_args (GICallableInfo *info)
   uint32_t offset;
   SignatureBlob *blob;
 
-  g_return_val_if_fail (info != NULL, -1);
-  g_return_val_if_fail (GI_IS_CALLABLE_INFO (info), -1);
+  g_return_val_if_fail (info != NULL, 0);
+  g_return_val_if_fail (GI_IS_CALLABLE_INFO (info), 0);
 
   offset = signature_offset (info);
   blob = (SignatureBlob *)&rinfo->typelib->data[offset];
@@ -710,7 +710,7 @@ gi_callable_info_invoke (GICallableInfo    *info,
     }
   for (i = 0; i < n_args; i++)
     {
-      int offset = (is_method ? 1 : 0);
+      size_t offset = (is_method ? 1 : 0);
       ainfo = gi_callable_info_get_arg ((GICallableInfo *)info, i);
       switch (gi_arg_info_get_direction (ainfo))
         {
diff --git a/girepository/giinterfaceinfo.c b/girepository/giinterfaceinfo.c
index 1c5289ea5..3901d2a25 100644
--- a/girepository/giinterfaceinfo.c
+++ b/girepository/giinterfaceinfo.c
@@ -149,7 +149,7 @@ gi_interface_info_get_property (GIInterfaceInfo *info,
   blob = (InterfaceBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->interface_blob_size
-    + (blob->n_prerequisites + (blob->n_prerequisites % 2)) * 2
+    + (blob->n_prerequisites + (blob->n_prerequisites % 2u)) * 2u
     + n * header->property_blob_size;
 
   return (GIPropertyInfo *) gi_base_info_new (GI_INFO_TYPE_PROPERTY, (GIBaseInfo*)info,
@@ -207,7 +207,7 @@ gi_interface_info_get_method (GIInterfaceInfo *info,
   blob = (InterfaceBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->interface_blob_size
-    + (blob->n_prerequisites + (blob->n_prerequisites % 2)) * 2
+    + (blob->n_prerequisites + (blob->n_prerequisites % 2u)) * 2u
     + blob->n_properties * header->property_blob_size
     + n * header->function_blob_size;
 
@@ -239,7 +239,7 @@ gi_interface_info_find_method (GIInterfaceInfo *info,
   InterfaceBlob *blob = (InterfaceBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->interface_blob_size
-    + (blob->n_prerequisites + (blob->n_prerequisites % 2)) * 2
+    + (blob->n_prerequisites + (blob->n_prerequisites % 2u)) * 2u
     + blob->n_properties * header->property_blob_size;
 
   return gi_base_info_find_method ((GIBaseInfo*)info, offset, blob->n_methods, name);
@@ -296,7 +296,7 @@ gi_interface_info_get_signal (GIInterfaceInfo *info,
   blob = (InterfaceBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->interface_blob_size
-    + (blob->n_prerequisites + (blob->n_prerequisites % 2)) * 2
+    + (blob->n_prerequisites + (blob->n_prerequisites % 2u)) * 2u
     + blob->n_properties * header->property_blob_size
     + blob->n_methods * header->function_blob_size
     + n * header->signal_blob_size;
@@ -392,7 +392,7 @@ gi_interface_info_get_vfunc (GIInterfaceInfo *info,
   blob = (InterfaceBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->interface_blob_size
-    + (blob->n_prerequisites + (blob->n_prerequisites % 2)) * 2
+    + (blob->n_prerequisites + (blob->n_prerequisites % 2u)) * 2u
     + blob->n_properties * header->property_blob_size
     + blob->n_methods * header->function_blob_size
     + blob->n_signals * header->signal_blob_size
@@ -433,7 +433,7 @@ gi_interface_info_find_vfunc (GIInterfaceInfo *info,
   blob = (InterfaceBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->interface_blob_size
-    + (blob->n_prerequisites + blob->n_prerequisites % 2) * 2
+    + (blob->n_prerequisites + blob->n_prerequisites % 2u) * 2u
     + blob->n_properties * header->property_blob_size
     + blob->n_methods * header->function_blob_size
     + blob->n_signals * header->signal_blob_size;
@@ -492,7 +492,7 @@ gi_interface_info_get_constant (GIInterfaceInfo *info,
   blob = (InterfaceBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->interface_blob_size
-    + (blob->n_prerequisites + (blob->n_prerequisites % 2)) * 2
+    + (blob->n_prerequisites + (blob->n_prerequisites % 2u)) * 2u
     + blob->n_properties * header->property_blob_size
     + blob->n_methods * header->function_blob_size
     + blob->n_signals * header->signal_blob_size
diff --git a/girepository/giobjectinfo.c b/girepository/giobjectinfo.c
index 68cee822f..9dbcb5690 100644
--- a/girepository/giobjectinfo.c
+++ b/girepository/giobjectinfo.c
@@ -70,7 +70,7 @@ gi_object_info_get_field_offset (GIObjectInfo *info,
   FieldBlob *field_blob;
 
   offset = rinfo->offset + header->object_blob_size
-    + (blob->n_interfaces + blob->n_interfaces % 2) * 2;
+    + (blob->n_interfaces + blob->n_interfaces % 2u) * 2u;
 
   for (size_t i = 0; i < n; i++)
     {
@@ -383,7 +383,7 @@ gi_object_info_get_property (GIObjectInfo *info,
   blob = (ObjectBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->object_blob_size
-    + (blob->n_interfaces + blob->n_interfaces % 2) * 2
+    + (blob->n_interfaces + blob->n_interfaces % 2u) * 2u
     + blob->n_fields * header->field_blob_size
     + blob->n_field_callbacks * header->callback_blob_size
     + n * header->property_blob_size;
@@ -444,7 +444,7 @@ gi_object_info_get_method (GIObjectInfo *info,
 
 
   offset = rinfo->offset + header->object_blob_size
-    + (blob->n_interfaces + blob->n_interfaces % 2) * 2
+    + (blob->n_interfaces + blob->n_interfaces % 2u) * 2u
     + blob->n_fields * header->field_blob_size
     + blob->n_field_callbacks * header->callback_blob_size
     + blob->n_properties * header->property_blob_size
@@ -484,7 +484,7 @@ gi_object_info_find_method (GIObjectInfo *info,
   blob = (ObjectBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->object_blob_size
-    + (blob->n_interfaces + blob->n_interfaces % 2) * 2
+    + (blob->n_interfaces + blob->n_interfaces % 2u) * 2u
     + blob->n_fields * header->field_blob_size +
     + blob->n_field_callbacks * header->callback_blob_size
     + blob->n_properties * header->property_blob_size;
@@ -528,8 +528,7 @@ gi_object_info_find_method_using_interfaces (GIObjectInfo  *info,
 
   if (result == NULL)
     {
-      int n_interfaces;
-      int i;
+      unsigned int n_interfaces, i;
 
       n_interfaces = gi_object_info_get_n_interfaces (info);
       for (i = 0; i < n_interfaces; ++i)
@@ -588,7 +587,7 @@ object_get_signal_offset (GIObjectInfo *info, unsigned int n)
   ObjectBlob *blob = (ObjectBlob *) &rinfo->typelib->data[rinfo->offset];
 
   return rinfo->offset + header->object_blob_size
-    + (blob->n_interfaces + blob->n_interfaces % 2) * 2
+    + (blob->n_interfaces + blob->n_interfaces % 2u) * 2u
     + blob->n_fields * header->field_blob_size
     + blob->n_field_callbacks * header->callback_blob_size
     + blob->n_properties * header->property_blob_size
@@ -723,7 +722,7 @@ gi_object_info_get_vfunc (GIObjectInfo *info,
   blob = (ObjectBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->object_blob_size
-    + (blob->n_interfaces + blob->n_interfaces % 2) * 2
+    + (blob->n_interfaces + blob->n_interfaces % 2u) * 2u
     + blob->n_fields * header->field_blob_size
     + blob->n_field_callbacks * header->callback_blob_size
     + blob->n_properties * header->property_blob_size
@@ -771,7 +770,7 @@ gi_object_info_find_vfunc (GIObjectInfo *info,
   blob = (ObjectBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->object_blob_size
-    + (blob->n_interfaces + blob->n_interfaces % 2) * 2
+    + (blob->n_interfaces + blob->n_interfaces % 2u) * 2u
     + blob->n_fields * header->field_blob_size
     + blob->n_field_callbacks * header->callback_blob_size
     + blob->n_properties * header->property_blob_size
@@ -822,8 +821,7 @@ gi_object_info_find_vfunc_using_interfaces (GIObjectInfo  *info,
 
   if (result == NULL)
     {
-      int n_interfaces;
-      int i;
+      unsigned int n_interfaces, i;
 
       n_interfaces = gi_object_info_get_n_interfaces (info);
       for (i = 0; i < n_interfaces; ++i)
@@ -902,7 +900,7 @@ gi_object_info_get_constant (GIObjectInfo *info,
   blob = (ObjectBlob *)&rinfo->typelib->data[rinfo->offset];
 
   offset = rinfo->offset + header->object_blob_size
-    + (blob->n_interfaces + blob->n_interfaces % 2) * 2
+    + (blob->n_interfaces + blob->n_interfaces % 2u) * 2u
     + blob->n_fields * header->field_blob_size
     + blob->n_field_callbacks * header->callback_blob_size
     + blob->n_properties * header->property_blob_size
diff --git a/girepository/girepository.c b/girepository/girepository.c
index eefe52928..8d65b6258 100644
--- a/girepository/girepository.c
+++ b/girepository/girepository.c
@@ -604,7 +604,8 @@ load_dependencies_recurse (GIRepository *repository,
           const char *dependency_version;
 
           last_dash = strrchr (dependency, '-');
-          dependency_namespace = g_strndup (dependency, last_dash - dependency);
+          g_assert (last_dash != NULL);  /* get_typelib_dependencies() guarantees this */
+          dependency_namespace = g_strndup (dependency, (size_t) (last_dash - dependency));
           dependency_version = last_dash+1;
 
           if (!gi_repository_require (repository, dependency_namespace, dependency_version,
@@ -782,7 +783,8 @@ get_typelib_dependencies_transitive (GIRepository *repository,
 
       /* Recurse for this namespace. */
       last_dash = strrchr (dependency, '-');
-      dependency_namespace = g_strndup (dependency, last_dash - dependency);
+      g_assert (last_dash != NULL);  /* get_typelib_dependencies() guarantees this */
+      dependency_namespace = g_strndup (dependency, (size_t) (last_dash - dependency));
 
       typelib = get_registered (repository, dependency_namespace, NULL);
       g_return_if_fail (typelib != NULL);
@@ -973,12 +975,12 @@ gi_repository_get_n_infos (GIRepository *repository,
   GITypelib *typelib;
   unsigned int n_interfaces = 0;
 
-  g_return_val_if_fail (GI_IS_REPOSITORY (repository), -1);
-  g_return_val_if_fail (namespace != NULL, -1);
+  g_return_val_if_fail (GI_IS_REPOSITORY (repository), 0);
+  g_return_val_if_fail (namespace != NULL, 0);
 
   typelib = get_registered (repository, namespace, NULL);
 
-  g_return_val_if_fail (typelib != NULL, -1);
+  g_return_val_if_fail (typelib != NULL, 0);
 
   n_interfaces = ((Header *)typelib->data)->n_local_entries;
 
@@ -1739,7 +1741,12 @@ enumerate_namespace_versions (const char         *namespace,
 
               name_end = strrchr (entry, '.');
               last_dash = strrchr (entry, '-');
-              version = g_strndup (last_dash+1, name_end-(last_dash+1));
+
+              /* These are guaranteed by the suffix and prefix checks above: */
+              g_assert (name_end != NULL);
+              g_assert (last_dash != NULL);
+
+              version = g_strndup (last_dash + 1, (size_t) (name_end - (last_dash + 1u)));
               if (!parse_version (version, &major, &minor))
                 {
                   g_free (version);
diff --git a/girepository/girmodule.c b/girepository/girmodule.c
index 87bb13ad3..96a878388 100644
--- a/girepository/girmodule.c
+++ b/girepository/girmodule.c
@@ -250,7 +250,7 @@ node_cmp_offset_func (const void *a,
 {
   const GIIrNode *na = a;
   const GIIrNode *nb = b;
-  return na->offset - nb->offset;
+  return (int) na->offset - (int) nb->offset;
 }
 
 static void
diff --git a/girepository/girnode.c b/girepository/girnode.c
index 65641625d..eaced1561 100644
--- a/girepository/girnode.c
+++ b/girepository/girnode.c
@@ -1523,8 +1523,6 @@ gi_ir_node_build_typelib (GIIrNode         *node,
                         array->dimensions.length = type->length;
                       else if (array->has_size)
                         array->dimensions.size  = type->size;
-                      else
-                        array->dimensions.length = -1;
 
                       pos = *offset2 + G_STRUCT_OFFSET (ArrayTypeBlob, type);
                       *offset2 += sizeof (ArrayTypeBlob);
@@ -2197,7 +2195,8 @@ gi_ir_node_build_typelib (GIIrNode         *node,
         blob->n_fields = 0;
         blob->n_functions = 0;
 
-        blob->discriminator_offset = union_->discriminator_offset;
+        g_assert (union_->discriminator_offset <= G_MAXINT32);
+        blob->discriminator_offset = (int32_t) union_->discriminator_offset;
 
         if (union_->copy_func)
           blob->copy_func = gi_ir_write_string (union_->copy_func, strings, data, offset2);
diff --git a/girepository/giroffsets.c b/girepository/giroffsets.c
index d3fe36a1d..60e6e341f 100644
--- a/girepository/giroffsets.c
+++ b/girepository/giroffsets.c
@@ -356,7 +356,7 @@ get_field_size_alignment (GIIrTypelibBuild *build,
   return success;
 }
 
-#define GI_ALIGN(n, align) (((n) + (align) - 1) & ~((align) - 1))
+#define GI_ALIGN(n, align) (((n) + (align) - 1u) & ~((align) - 1u))
 
 static gboolean
 compute_struct_field_offsets (GIIrTypelibBuild *build,
diff --git a/girepository/girparser.c b/girepository/girparser.c
index ab8d46bcc..52e6a92fa 100644
--- a/girepository/girparser.c
+++ b/girepository/girparser.c
@@ -454,11 +454,12 @@ push_node (ParseContext *ctx, GIIrNode *node)
   ctx->node_stack = g_slist_prepend (ctx->node_stack, node);
 }
 
-static GIIrNodeType * parse_type_internal (GIIrModule *module,
-                                           const char *str,
-                                           char **next,
-                                           gboolean in_glib,
-                                           gboolean in_gobject);
+static GIIrNodeType * parse_type_internal (GIIrModule  *module,
+                                           const char  *str,
+                                           char       **next,
+                                           gboolean     in_glib,
+                                           gboolean     in_gobject,
+                                           GError     **error);
 
 typedef struct {
   const char *str;
@@ -575,11 +576,12 @@ parse_basic (const char *str)
 }
 
 static GIIrNodeType *
-parse_type_internal (GIIrModule   *module,
-                     const char   *str,
-                     char        **next,
-                     gboolean      in_glib,
-                     gboolean      in_gobject)
+parse_type_internal (GIIrModule  *module,
+                     const char  *str,
+                     char       **next,
+                     gboolean     in_glib,
+                     gboolean     in_gobject,
+                     GError     **error)
 {
   const BasicTypeInfo *basic;
   GIIrNodeType *type;
@@ -685,7 +687,14 @@ parse_type_internal (GIIrModule   *module,
           (str)++;
 
           end = strchr (str, '>');
-          tmp = g_strndup (str, end - str);
+          if (end == NULL)
+            {
+              g_set_error (error, G_MARKUP_ERROR,
+                           G_MARKUP_ERROR_INVALID_CONTENT,
+                           "Failed to parse type ‘%s’", type->unparsed);
+              goto error;
+            }
+          tmp = g_strndup (str, (size_t) (end - str));
           type->errors = g_strsplit (tmp, ",", 0);
           g_free (tmp);
 
@@ -707,7 +716,7 @@ parse_type_internal (GIIrModule   *module,
              *str == ':')
         (str)++;
 
-      type->giinterface = g_strndup (start, str - start);
+      type->giinterface = g_strndup (start, (size_t) (str - start));
     }
 
   if (next)
@@ -716,7 +725,8 @@ parse_type_internal (GIIrModule   *module,
   g_free (temporary_type);
   return type;
 
-/* error: */
+error:
+  g_assert (error == NULL || *error != NULL);
   gi_ir_node_free ((GIIrNode *)type);
   g_free (temporary_type);
   return NULL;
@@ -791,7 +801,9 @@ is_pointer_or_disguised_structure (ParseContext *ctx,
 }
 
 static GIIrNodeType *
-parse_type (ParseContext *ctx, const char *type)
+parse_type (ParseContext  *ctx,
+            const char    *type,
+            GError       **error)
 {
   GIIrNodeType *node;
   const BasicTypeInfo *basic;
@@ -805,11 +817,11 @@ parse_type (ParseContext *ctx, const char *type)
   if (basic == NULL)
     type = resolve_aliases (ctx, type);
 
-  node = parse_type_internal (ctx->current_module, type, NULL, in_glib, in_gobject);
+  node = parse_type_internal (ctx->current_module, type, NULL, in_glib, in_gobject, error);
   if (node)
     g_debug ("Parsed type: %s => %d", type, node->tag);
   else
-    g_critical ("Failed to parse type: '%s'", type);
+    g_debug ("Failed to parse type: '%s'", type);
 
   return node;
 }
@@ -1517,7 +1529,8 @@ start_field (GMarkupParseContext  *context,
     }
   else
     {
-      field->type = parse_type (ctx, "gpointer");
+      field->type = parse_type (ctx, "gpointer", NULL);
+      g_assert (field->type != NULL);  /* parsing `gpointer` should never fail */
     }
 
   ((GIIrNode *)field)->name = g_strdup (name);
@@ -2211,22 +2224,20 @@ start_type (GMarkupParseContext  *context,
           size = find_attribute ("fixed-size", attribute_names, attribute_values);
 
           typenode->has_length = len != NULL;
-          if (!typenode->has_length)
-            typenode->length = -1;
-          else if (g_ascii_string_to_unsigned (len, 10, 0, G_MAXUINT, &parsed_uint, error))
+          if (typenode->has_length &&
+              g_ascii_string_to_unsigned (len, 10, 0, G_MAXUINT, &parsed_uint, error))
             typenode->length = parsed_uint;
-          else
+          else if (typenode->has_length)
             {
               gi_ir_node_free ((GIIrNode *) typenode);
               return FALSE;
             }
 
           typenode->has_size = size != NULL;
-          if (!typenode->has_size)
-            typenode->size = -1;
-          else if (g_ascii_string_to_unsigned (size, 10, 0, G_MAXSIZE, &parsed_uint, error))
+          if (typenode->has_size &&
+              g_ascii_string_to_unsigned (size, 10, 0, G_MAXSIZE, &parsed_uint, error))
             typenode->size = parsed_uint;
-          else
+          else if (typenode->has_size)
             {
               gi_ir_node_free ((GIIrNode *) typenode);
               return FALSE;
@@ -2243,9 +2254,7 @@ start_type (GMarkupParseContext  *context,
         } else {
           typenode->zero_terminated = FALSE;
           typenode->has_length = FALSE;
-          typenode->length = -1;
           typenode->has_size = FALSE;
-          typenode->size = -1;
         }
     }
   else
@@ -2276,7 +2285,9 @@ start_type (GMarkupParseContext  *context,
           pointer_depth > 0)
         pointer_depth--;
 
-      typenode = parse_type (ctx, name);
+      typenode = parse_type (ctx, name, error);
+      if (typenode == NULL)
+        return FALSE;
 
       /* A "pointer" structure is one where the c:type is a typedef that
        * to a pointer to a structure; we used to call them "disguised"
@@ -2320,14 +2331,17 @@ end_type_top (ParseContext *ctx)
       typenode->tag == GI_TYPE_TAG_GSLIST)
     {
       if (typenode->parameter_type1 == NULL)
-        typenode->parameter_type1 = parse_type (ctx, "gpointer");
+        typenode->parameter_type1 = parse_type (ctx, "gpointer", NULL);
+      g_assert (typenode->parameter_type1 != NULL);  /* parsing `gpointer` should never fail */
     }
   else if (typenode->tag == GI_TYPE_TAG_GHASH)
     {
       if (typenode->parameter_type1 == NULL)
         {
-          typenode->parameter_type1 = parse_type (ctx, "gpointer");
-          typenode->parameter_type2 = parse_type (ctx, "gpointer");
+          typenode->parameter_type1 = parse_type (ctx, "gpointer", NULL);
+          g_assert (typenode->parameter_type1 != NULL);  /* parsing `gpointer` should never fail */
+          typenode->parameter_type2 = parse_type (ctx, "gpointer", NULL);
+          g_assert (typenode->parameter_type2 != NULL);  /* same */
         }
     }
 
@@ -2977,6 +2991,7 @@ start_discriminator (GMarkupParseContext  *context,
   const char *type;
   const char *offset;
   guint64 parsed_offset;
+  GIIrNodeType *discriminator_type = NULL;
 
   if (!(strcmp (element_name, "discriminator") == 0 &&
         ctx->state == STATE_UNION))
@@ -2995,8 +3010,11 @@ start_discriminator (GMarkupParseContext  *context,
       return FALSE;
     }
 
-  ((GIIrNodeUnion *)CURRENT_NODE (ctx))->discriminator_type
-    = parse_type (ctx, type);
+  discriminator_type = parse_type (ctx, type, error);
+  if (discriminator_type == NULL)
+    return FALSE;
+
+  ((GIIrNodeUnion *)CURRENT_NODE (ctx))->discriminator_type = g_steal_pointer (&discriminator_type);
 
   if (g_ascii_string_to_unsigned (offset, 10, 0, G_MAXSIZE, &parsed_offset, error))
     ((GIIrNodeUnion *)CURRENT_NODE (ctx))->discriminator_offset = parsed_offset;
@@ -3062,7 +3080,14 @@ parse_include (GMarkupParseContext *context,
       return FALSE;
     }
 
-  module = gi_ir_parser_parse_string (ctx->parser, name, girpath, buffer, length, &error);
+  if (length > G_MAXSSIZE)
+    {
+      g_printerr ("Input file ‘%s’ too big\n", girpath);
+      g_free (girpath);
+      return FALSE;
+    }
+
+  module = gi_ir_parser_parse_string (ctx->parser, name, girpath, buffer, (gssize) length, &error);
   g_free (buffer);
   if (error != NULL)
     {
@@ -3904,7 +3929,7 @@ cleanup (GMarkupParseContext *context,
  * @namespace: the namespace of the string
  * @filename: (nullable) (type filename): Path to parsed file, or `NULL`
  * @buffer: (array length=length): the data containing the XML
- * @length: length of the data, in bytes
+ * @length: length of the data, in bytes, or `-1` if nul terminated
  * @error: return location for a [type@GLib.Error], or `NULL`
  *
  * Parse a string that holds a complete GIR XML file, and return a list of a
@@ -4043,7 +4068,19 @@ gi_ir_parser_parse_file (GIIrParser   *parser,
       return NULL;
     }
 
-  module = gi_ir_parser_parse_string (parser, namespace, filename, buffer, length, error);
+  if (length > G_MAXSSIZE)
+    {
+      g_free (namespace);
+      g_free (buffer);
+
+      g_set_error (error,
+                   G_MARKUP_ERROR,
+                   G_MARKUP_ERROR_INVALID_CONTENT,
+                   "Input file too big");
+      return NULL;
+    }
+
+  module = gi_ir_parser_parse_string (parser, namespace, filename, buffer, (gssize) length, error);
 
   g_free (namespace);
 
diff --git a/girepository/gitypelib.c b/girepository/gitypelib.c
index 57411a86b..68247dd36 100644
--- a/girepository/gitypelib.c
+++ b/girepository/gitypelib.c
@@ -87,7 +87,7 @@ get_dir_entry_checked (GITypelib *typelib,
       return FALSE;
     }
 
-  offset = header->directory + (index - 1) * header->entry_blob_size;
+  offset = header->directory + (index - 1u) * header->entry_blob_size;
 
   if (typelib->len < offset + sizeof (DirEntry))
     {
@@ -161,7 +161,8 @@ gi_typelib_get_dir_entry (GITypelib *typelib,
 {
   Header *header = (Header *)typelib->data;
 
-  return (DirEntry *)&typelib->data[header->directory + (index - 1) * header->entry_blob_size];
+  /* this deliberately doesn’t check for underflow of @index; see get_dir_entry_checked() for that */
+  return (DirEntry *)&typelib->data[header->directory + (index - 1u) * header->entry_blob_size];
 }
 
 static Section *
@@ -303,7 +304,7 @@ strsplit_iter_next (StrSplitIter  *iter,
   if (next)
     {
       iter->s = next + iter->sep_len;
-      len = next - s;
+      len = (size_t) (next - s);
     }
   else
     {
@@ -1718,7 +1719,7 @@ validate_object_blob (ValidateContext *ctx,
     }
 
   if (typelib->len < offset + sizeof (ObjectBlob) +
-            (blob->n_interfaces + blob->n_interfaces % 2) * 2 +
+            (blob->n_interfaces + blob->n_interfaces % 2u) * 2u +
             blob->n_fields * sizeof (FieldBlob) +
             blob->n_properties * sizeof (PropertyBlob) +
             blob->n_methods * sizeof (FunctionBlob) +
@@ -1875,7 +1876,7 @@ validate_interface_blob (ValidateContext *ctx,
     return FALSE;
 
   if (typelib->len < offset + sizeof (InterfaceBlob) +
-            (blob->n_prerequisites + blob->n_prerequisites % 2) * 2 +
+            (blob->n_prerequisites + blob->n_prerequisites % 2u) * 2u +
             blob->n_properties * sizeof (PropertyBlob) +
             blob->n_methods * sizeof (FunctionBlob) +
             blob->n_signals * sizeof (SignalBlob) +
diff --git a/girepository/giunioninfo.c b/girepository/giunioninfo.c
index de9a34bed..8a1e28723 100644
--- a/girepository/giunioninfo.c
+++ b/girepository/giunioninfo.c
@@ -169,7 +169,7 @@ gi_union_info_get_discriminator_offset (GIUnionInfo *info,
   UnionBlob *blob = (UnionBlob *)&rinfo->typelib->data[rinfo->offset];
   size_t discriminator_offset;
 
-  discriminator_offset = (blob->discriminated) ? blob->discriminator_offset : 0;
+  discriminator_offset = (blob->discriminated) ? (size_t) blob->discriminator_offset : 0;
 
   if (out_offset != NULL)
     *out_offset = discriminator_offset;
diff --git a/girepository/givfuncinfo.c b/girepository/givfuncinfo.c
index 728cca43c..4cd328bba 100644
--- a/girepository/givfuncinfo.c
+++ b/girepository/givfuncinfo.c
@@ -224,7 +224,8 @@ gi_vfunc_info_get_address (GIVFuncInfo  *vfunc_info,
   GIObjectInfo *object_info;
   GIStructInfo *struct_info;
   GIFieldInfo *field_info = NULL;
-  int length, i, offset;
+  size_t offset;
+  unsigned int length, i;
   void *implementor_class, *implementor_vtable;
   void *func = NULL;
 
diff --git a/girepository/inspector/meson.build b/girepository/inspector/meson.build
index 8948cedc8..4467e6df8 100644
--- a/girepository/inspector/meson.build
+++ b/girepository/inspector/meson.build
@@ -3,6 +3,7 @@
 
 custom_c_args = [
   '-DG_LOG_DOMAIN="GLib-GirInspector"',
+  warning_sign_conversion_args,
 ]
 
 if cc.get_id() != 'msvc'
diff --git a/girepository/meson.build b/girepository/meson.build
index 3010099aa..b08801891 100644
--- a/girepository/meson.build
+++ b/girepository/meson.build
@@ -89,6 +89,7 @@ gir_c_args = [
   '-DGOBJECT_INTROSPECTION_LIBDIR="@0@"'.format(glib_libdir),
   '-DGOBJECT_INTROSPECTION_DATADIR="@0@"'.format(glib_datadir),
   '-DGOBJECT_INTROSPECTION_RELATIVE_LIBDIR="@0@"'.format(get_option('libdir')),
+  warning_sign_conversion_args,
 ]
 
 custom_c_args = []
diff --git a/girepository/tests/ir-parser.c b/girepository/tests/ir-parser.c
new file mode 100644
index 000000000..79b71ab88
--- /dev/null
+++ b/girepository/tests/ir-parser.c
@@ -0,0 +1,106 @@
+/*
+ * Copyright 2025 GNOME Foundation, Inc.
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General
+ * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors:
+ *  - Philip Withnall <pwithnall@gnome.org>
+ */
+
+#include "config.h"
+
+#include "girepository.h"
+#include "girparser-private.h"
+
+static void
+test_type_parsing (void)
+{
+  const char *buffer_template = "<?xml version='1.0'?>"
+    "<repository version='1.2'"
+    "   xmlns='http://www.gtk.org/introspection/core/1.0'"
+    "   xmlns:c='http://www.gtk.org/introspection/c/1.0'>"
+      "<package name='TestNamespace-1.0'/>"
+      "<namespace name='TestNamespace' version='1.0'"
+      "   c:identifier-prefixes='test'"
+      "   c:symbol-prefixes='test'>"
+        "<function name='dummy' c:identifier='dummy'>"
+          "<return-value transfer-ownership='none'>"
+            "<type name='%s'/>"
+          "</return-value>"
+          "<parameters>"
+          "</parameters>"
+        "</function>"
+      "</namespace>"
+    "</repository>";
+  const struct
+    {
+      const char *type;
+      gboolean expected_success;
+    }
+  vectors[] =
+    {
+      { "GLib.Error", TRUE },
+      { "GLib.Error<IOError,FileError>", TRUE },
+      { "GLib.Error<IOError", FALSE },
+    };
+
+  g_test_summary ("Test parsing different valid and invalid types");
+
+  for (size_t i = 0; i < G_N_ELEMENTS (vectors); i++)
+    {
+      GIIrParser *parser = NULL;
+      GIIrModule *module;
+      GError *local_error = NULL;
+      char *buffer = NULL;
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wformat-nonliteral"
+      buffer = g_strdup_printf (buffer_template, vectors[i].type);
+#pragma GCC diagnostic pop
+
+      parser = gi_ir_parser_new ();
+      module = gi_ir_parser_parse_string (parser, "TestNamespace",
+                                          "TestNamespace-1.0.gir",
+                                          buffer, -1,
+                                          &local_error);
+
+      if (vectors[i].expected_success)
+        {
+          g_assert_no_error (local_error);
+          g_assert_nonnull (module);
+        }
+      else
+        {
+          g_assert_error (local_error, G_MARKUP_ERROR, G_MARKUP_ERROR_INVALID_CONTENT);
+          g_assert_null (module);
+        }
+
+      g_clear_error (&local_error);
+      g_clear_pointer (&parser, gi_ir_parser_free);
+      g_free (buffer);
+    }
+}
+
+int
+main (int argc,
+      char *argv[])
+{
+  g_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/ir-parser/type-parsing", test_type_parsing);
+
+  return g_test_run ();
+}
diff --git a/girepository/tests/meson.build b/girepository/tests/meson.build
index ab5e9f748..0697c9fa2 100644
--- a/girepository/tests/meson.build
+++ b/girepository/tests/meson.build
@@ -50,6 +50,9 @@ if enable_gir
       'dependencies': [libffi_dep],
       'depends': glib_gir_testing_dep,
     },
+    'ir-parser' : {
+      'dependencies': [libgirepository_internals_dep],
+    },
     'object-info' : {
       'depends': gio_gir_testing_dep,
     },
@@ -91,7 +94,7 @@ test_env.set('G_TEST_SRCDIR', meson.current_source_dir())
 test_env.set('G_TEST_BUILDDIR', meson.current_build_dir())
 
 test_deps = [libm, thread_dep, libgirepository_dep]
-test_cargs = ['-DG_LOG_DOMAIN="GIRepository"', '-UG_DISABLE_ASSERT']
+test_cargs = ['-DG_LOG_DOMAIN="GIRepository"', '-UG_DISABLE_ASSERT', warning_sign_conversion_args]
 test_cpp_args = test_cargs
 
 foreach test_name, extra_args : girepository_tests
diff --git a/gmodule/gmodule-win32.c b/gmodule/gmodule-win32.c
index 5748bef0f..3869d3dae 100644
--- a/gmodule/gmodule-win32.c
+++ b/gmodule/gmodule-win32.c
@@ -52,7 +52,7 @@ set_error (GError      **error,
   gchar *message;
   va_list args;
 
-  win32_error = g_win32_error_message (GetLastError ());
+  win32_error = g_win32_error_message ((gint) GetLastError ());
 
   va_start (args, format);
   detail = g_strdup_vprintf (format, args);
diff --git a/gmodule/gmodule.c b/gmodule/gmodule.c
index f0ba81b2e..8bdcd9da0 100644
--- a/gmodule/gmodule.c
+++ b/gmodule/gmodule.c
@@ -481,7 +481,7 @@ g_module_open_full (const gchar   *file_name,
     _g_module_debug_init ();
 
   if (module_debug_flags & G_MODULE_DEBUG_BIND_NOW_MODULES)
-    flags &= ~G_MODULE_BIND_LAZY;
+    flags &= (unsigned) ~G_MODULE_BIND_LAZY;
 
   if (!file_name)
     {      
diff --git a/gmodule/meson.build b/gmodule/meson.build
index f91924635..37a8fa42d 100644
--- a/gmodule/meson.build
+++ b/gmodule/meson.build
@@ -96,7 +96,7 @@ libgmodule = library('gmodule-2.0',
   install : true,
   include_directories : [configinc, gmoduleinc],
   dependencies : [libdl_dep, libglib_dep],
-  c_args : ['-DG_LOG_DOMAIN="GModule"', '-DGMODULE_COMPILATION'],
+  c_args : ['-DG_LOG_DOMAIN="GModule"', '-DGMODULE_COMPILATION', warning_sign_conversion_args],
   gnu_symbol_visibility : 'hidden',
   link_args : [glib_link_flags],
 )
diff --git a/gmodule/tests/meson.build b/gmodule/tests/meson.build
index 5374c1c2a..e7d7b3dd1 100644
--- a/gmodule/tests/meson.build
+++ b/gmodule/tests/meson.build
@@ -75,7 +75,7 @@ test_env.set('G_TEST_SRCDIR', meson.current_source_dir())
 test_env.set('G_TEST_BUILDDIR', meson.current_build_dir())
 
 test_deps = [libm, thread_dep, libglib_dep, libgmodule_dep]
-test_cargs = ['-DG_LOG_DOMAIN="GModule"', '-UG_DISABLE_ASSERT']
+test_cargs = ['-DG_LOG_DOMAIN="GModule"', '-UG_DISABLE_ASSERT', warning_sign_conversion_args]
 test_cpp_args = test_cargs
 
 foreach test_name, extra_args : gmodule_tests
diff --git a/gthread/meson.build b/gthread/meson.build
index abb6f9151..9b492eed6 100644
--- a/gthread/meson.build
+++ b/gthread/meson.build
@@ -19,7 +19,7 @@ libgthread = library('gthread-2.0',
   darwin_versions : darwin_versions,
   install : true,
   dependencies : [libglib_dep],
-  c_args : ['-DG_LOG_DOMAIN="GThread"', glib_c_args_internal],
+  c_args : ['-DG_LOG_DOMAIN="GThread"', glib_c_args_internal, warning_sign_conversion_args],
   gnu_symbol_visibility : 'hidden',
   link_args : glib_link_flags,
 )
diff --git a/gthread/tests/meson.build b/gthread/tests/meson.build
index 41fad1de4..66b50caf7 100644
--- a/gthread/tests/meson.build
+++ b/gthread/tests/meson.build
@@ -7,7 +7,7 @@ test_env.set('G_TEST_SRCDIR', meson.current_source_dir())
 test_env.set('G_TEST_BUILDDIR', meson.current_build_dir())
 
 test_deps = [thread_dep, libglib_dep, libgthread_dep]
-test_cargs = ['-DG_LOG_DOMAIN="GLib-GThread"', '-UG_DISABLE_ASSERT']
+test_cargs = ['-DG_LOG_DOMAIN="GLib-GThread"', '-UG_DISABLE_ASSERT', warning_sign_conversion_args]
 test_cpp_args = test_cargs
 
 foreach test_name, extra_args : gthread_tests