diff --git a/gio/gmemorymonitor.c b/gio/gmemorymonitor.c
index ae0d3f7ce..37ddf48ca 100644
--- a/gio/gmemorymonitor.c
+++ b/gio/gmemorymonitor.c
@@ -118,7 +118,7 @@ static guint signals[LAST_SIGNAL] = { 0 };
  *
  * Gets a reference to the default #GMemoryMonitor for the system.
  *
- * Returns: (transfer full): a new reference to the default #GMemoryMonitor
+ * Returns: (not nullable) (transfer full): a new reference to the default #GMemoryMonitor
  *
  * Since: 2.64
  */
diff --git a/gio/gnetworkmonitor.c b/gio/gnetworkmonitor.c
index f9853fca5..8027e4663 100644
--- a/gio/gnetworkmonitor.c
+++ b/gio/gnetworkmonitor.c
@@ -83,7 +83,8 @@ static guint signals[LAST_SIGNAL] = { 0 };
  *
  * Gets the default #GNetworkMonitor for the system.
  *
- * Returns: (transfer none): a #GNetworkMonitor
+ * Returns: (not nullable) (transfer none): a #GNetworkMonitor, which will be
+ *     a dummy object if no network monitor is available
  *
  * Since: 2.32
  */
diff --git a/gio/gproxyresolver.c b/gio/gproxyresolver.c
index ca346633a..c83347b52 100644
--- a/gio/gproxyresolver.c
+++ b/gio/gproxyresolver.c
@@ -72,7 +72,8 @@ g_proxy_resolver_default_init (GProxyResolverInterface *iface)
  *
  * Gets the default #GProxyResolver for the system.
  *
- * Returns: (transfer none): the default #GProxyResolver.
+ * Returns: (not nullable) (transfer none): the default #GProxyResolver, which
+ *     will be a dummy object if no proxy resolver is available
  *
  * Since: 2.26
  */
diff --git a/gio/gsettingsbackend.c b/gio/gsettingsbackend.c
index f53a02392..dcc7c3714 100644
--- a/gio/gsettingsbackend.c
+++ b/gio/gsettingsbackend.c
@@ -1001,7 +1001,9 @@ g_settings_backend_verify (gpointer impl)
  *
  * The user gets a reference to the backend.
  *
- * Returns: (transfer full): the default #GSettingsBackend
+ * Returns: (not nullable) (transfer full): the default #GSettingsBackend,
+ *     which will be a dummy (memory) settings backend if no other settings
+ *     backend is available.
  *
  * Since: 2.28
  */
diff --git a/gio/gtlsbackend.c b/gio/gtlsbackend.c
index d67e49012..6d948adf1 100644
--- a/gio/gtlsbackend.c
+++ b/gio/gtlsbackend.c
@@ -98,7 +98,8 @@ g_tls_backend_default_init (GTlsBackendInterface *iface)
  *
  * Gets the default #GTlsBackend for the system.
  *
- * Returns: (transfer none): a #GTlsBackend
+ * Returns: (not nullable) (transfer none): a #GTlsBackend, which will be a
+ *     dummy object if no TLS backend is available
  *
  * Since: 2.28
  */
diff --git a/gio/gvfs.c b/gio/gvfs.c
index 3475624cf..f178d7a41 100644
--- a/gio/gvfs.c
+++ b/gio/gvfs.c
@@ -342,7 +342,8 @@ g_vfs_parse_name (GVfs       *vfs,
  *
  * Gets the default #GVfs for the system.
  *
- * Returns: (transfer none): a #GVfs.
+ * Returns: (not nullable) (transfer none): a #GVfs, which will be the local
+ *     file system #GVfs if no other implementation is available.
  */
 GVfs *
 g_vfs_get_default (void)