diff --git a/clutter/clutter/clutter-debug.h b/clutter/clutter/clutter-debug.h
index 69d59502a..538f4a12e 100644
--- a/clutter/clutter/clutter-debug.h
+++ b/clutter/clutter/clutter-debug.h
@@ -80,9 +80,9 @@ extern guint clutter_pick_debug_flags;
 extern guint clutter_paint_debug_flags;
 
 void    _clutter_debug_messagev         (const char *format,
-                                         va_list     var_args);
+                                         va_list     var_args) G_GNUC_PRINTF (1, 0);
 void    _clutter_debug_message          (const char *format,
-                                         ...);
+                                         ...) G_GNUC_PRINTF (1, 2);
 
 G_END_DECLS
 
diff --git a/clutter/clutter/clutter-private.h b/clutter/clutter/clutter-private.h
index 129880dd9..f1b795290 100644
--- a/clutter/clutter/clutter-private.h
+++ b/clutter/clutter/clutter-private.h
@@ -202,7 +202,7 @@ gboolean      _clutter_feature_init (GError **error);
 
 /* Diagnostic mode */
 gboolean        _clutter_diagnostic_enabled     (void);
-void            _clutter_diagnostic_message     (const char *fmt, ...);
+void            _clutter_diagnostic_message     (const char *fmt, ...) G_GNUC_PRINTF (1, 2);
 
 /* Picking code */
 guint           _clutter_pixel_to_id            (guchar        pixel[4]);