diff --git a/glib/gmain.c b/glib/gmain.c
index 73b4ed93b..4d5a07d1d 100644
--- a/glib/gmain.c
+++ b/glib/gmain.c
@@ -290,6 +290,8 @@ struct _GSourcePrivate
    */
   GSList *fds;
 
+  GSourceFlags flags; /* atomic */
+
   GSourceDisposeFunc dispose;
 
   gboolean static_name;
@@ -307,8 +309,10 @@ typedef struct _GSourceIter
 #define UNLOCK_CONTEXT(context) g_mutex_unlock (&context->mutex)
 #define G_THREAD_SELF g_thread_self ()
 
-#define SOURCE_DESTROYED(source) (((source)->flags & G_HOOK_FLAG_ACTIVE) == 0)
-#define SOURCE_BLOCKED(source) (((source)->flags & G_SOURCE_BLOCKED) != 0)
+#define SOURCE_DESTROYED(source) \
+  ((g_atomic_int_get (&((source)->priv->flags)) & G_HOOK_FLAG_ACTIVE) == 0)
+#define SOURCE_BLOCKED(source) \
+  ((g_atomic_int_get (&((source)->priv->flags)) & G_SOURCE_BLOCKED) != 0)
 
 /* Forward declarations */
 
@@ -934,7 +938,7 @@ g_source_new (GSourceFuncs *source_funcs,
   
   source->priority = G_PRIORITY_DEFAULT;
 
-  source->flags = G_HOOK_FLAG_ACTIVE;
+  g_atomic_int_set (&source->priv->flags, G_HOOK_FLAG_ACTIVE);
 
   source->priv->ready_time = -1;
 
@@ -1284,8 +1288,8 @@ g_source_destroy_internal (GSource      *source,
       GSList *tmp_list;
       gpointer old_cb_data;
       GSourceCallbackFuncs *old_cb_funcs;
-      
-      source->flags &= ~G_HOOK_FLAG_ACTIVE;
+
+      g_atomic_int_and (&source->priv->flags, ~G_HOOK_FLAG_ACTIVE);
 
       old_cb_data = source->callback_data;
       old_cb_funcs = source->callback_funcs;
@@ -1359,7 +1363,7 @@ g_source_destroy (GSource *source)
   if (context)
     g_source_destroy_internal (source, context, FALSE);
   else
-    source->flags &= ~G_HOOK_FLAG_ACTIVE;
+    g_atomic_int_and (&source->priv->flags, ~G_HOOK_FLAG_ACTIVE);
 }
 
 /**
@@ -2007,9 +2011,9 @@ g_source_set_can_recurse (GSource  *source,
     LOCK_CONTEXT (context);
   
   if (can_recurse)
-    source->flags |= G_SOURCE_CAN_RECURSE;
+    g_atomic_int_or (&source->priv->flags, G_SOURCE_CAN_RECURSE);
   else
-    source->flags &= ~G_SOURCE_CAN_RECURSE;
+    g_atomic_int_and (&source->priv->flags, ~G_SOURCE_CAN_RECURSE);
 
   if (context)
     UNLOCK_CONTEXT (context);
@@ -2029,8 +2033,8 @@ g_source_get_can_recurse (GSource  *source)
 {
   g_return_val_if_fail (source != NULL, FALSE);
   g_return_val_if_fail (g_atomic_int_get (&source->ref_count) > 0, FALSE);
-  
-  return (source->flags & G_SOURCE_CAN_RECURSE) != 0;
+
+  return (g_atomic_int_get (&source->priv->flags) & G_SOURCE_CAN_RECURSE) != 0;
 }
 
 static void
@@ -3240,7 +3244,7 @@ block_source (GSource *source)
 
   g_return_if_fail (!SOURCE_BLOCKED (source));
 
-  source->flags |= G_SOURCE_BLOCKED;
+  g_atomic_int_or (&source->priv->flags, G_SOURCE_BLOCKED);
 
   if (source->context)
     {
@@ -3274,8 +3278,8 @@ unblock_source (GSource *source)
 
   g_return_if_fail (SOURCE_BLOCKED (source)); /* Source already unblocked */
   g_return_if_fail (!SOURCE_DESTROYED (source));
-  
-  source->flags &= ~G_SOURCE_BLOCKED;
+
+  g_atomic_int_and (&source->priv->flags, ~G_SOURCE_BLOCKED);
 
   tmp_list = source->poll_fds;
   while (tmp_list)
@@ -3312,7 +3316,7 @@ g_main_dispatch (GMainContext *context)
       context->pending_dispatches->pdata[i] = NULL;
       g_assert (source);
 
-      source->flags &= ~G_SOURCE_READY;
+      g_atomic_int_and (&source->priv->flags, ~G_SOURCE_READY);
 
       if (!SOURCE_DESTROYED (source))
 	{
@@ -3336,11 +3340,12 @@ g_main_dispatch (GMainContext *context)
 	  if (cb_funcs)
 	    cb_funcs->ref (cb_data);
 	  
-	  if ((source->flags & G_SOURCE_CAN_RECURSE) == 0)
+	  if ((g_atomic_int_get (&source->priv->flags) & G_SOURCE_CAN_RECURSE) == 0)
 	    block_source (source);
 	  
-	  was_in_call = source->flags & G_HOOK_FLAG_IN_CALL;
-	  source->flags |= G_HOOK_FLAG_IN_CALL;
+          was_in_call = g_atomic_int_or (&source->priv->flags,
+                                         (GSourceFlags) G_HOOK_FLAG_IN_CALL) &
+                                         G_HOOK_FLAG_IN_CALL;
 
 	  if (cb_funcs)
 	    cb_funcs->get (cb_data, source, &callback, &user_data);
@@ -3377,9 +3382,9 @@ g_main_dispatch (GMainContext *context)
  	  LOCK_CONTEXT (context);
 	  
 	  if (!was_in_call)
-	    source->flags &= ~G_HOOK_FLAG_IN_CALL;
+            g_atomic_int_and (&source->priv->flags, ~G_HOOK_FLAG_IN_CALL);
 
-	  if (SOURCE_BLOCKED (source) && !SOURCE_DESTROYED (source))
+          if (SOURCE_BLOCKED (source) && !SOURCE_DESTROYED (source))
 	    unblock_source (source);
 	  
 	  /* Note: this depends on the fact that we can't switch
@@ -3746,7 +3751,7 @@ g_main_context_prepare_unlocked (GMainContext *context,
       if ((n_ready > 0) && (source->priority > current_priority))
 	break;
 
-      if (!(source->flags & G_SOURCE_READY))
+      if (!(g_atomic_int_get (&source->priv->flags) & G_SOURCE_READY))
 	{
 	  gboolean result;
 	  gboolean (* prepare) (GSource  *source,
@@ -3807,13 +3812,13 @@ g_main_context_prepare_unlocked (GMainContext *context,
 
 	      while (ready_source)
 		{
-		  ready_source->flags |= G_SOURCE_READY;
+                  g_atomic_int_or (&ready_source->priv->flags, G_SOURCE_READY);
 		  ready_source = ready_source->priv->parent_source;
 		}
 	    }
 	}
 
-      if (source->flags & G_SOURCE_READY)
+      if (g_atomic_int_get (&source->priv->flags) & G_SOURCE_READY)
 	{
 	  n_ready++;
 	  current_priority = source->priority;
@@ -4079,8 +4084,8 @@ g_main_context_check_unlocked (GMainContext *context,
       if ((n_ready > 0) && (source->priority > max_priority))
 	break;
 
-      if (!(source->flags & G_SOURCE_READY))
-	{
+      if (!(g_atomic_int_get (&source->priv->flags) & G_SOURCE_READY))
+        {
           gboolean result;
           gboolean (* check) (GSource *source);
 
@@ -4150,13 +4155,13 @@ g_main_context_check_unlocked (GMainContext *context,
 
 	      while (ready_source)
 		{
-		  ready_source->flags |= G_SOURCE_READY;
+                  g_atomic_int_or (&ready_source->priv->flags, G_SOURCE_READY);
 		  ready_source = ready_source->priv->parent_source;
 		}
 	    }
 	}
 
-      if (source->flags & G_SOURCE_READY)
+      if (g_atomic_int_get (&source->priv->flags) & G_SOURCE_READY)
 	{
           g_source_ref (source);
 	  g_ptr_array_add (context->pending_dispatches, source);