diff --git a/widget/gtk2/Makefile.in b/widget/gtk2/Makefile.in
index 903286d02c9..25e1cfed0de 100644
--- a/widget/gtk2/Makefile.in
+++ b/widget/gtk2/Makefile.in
@@ -18,6 +18,7 @@ endif
 
 EXPORT_LIBRARY	= 1
 LIBXUL_LIBRARY = 1
+FAIL_ON_WARNINGS = 1
 
 NATIVE_THEME_SUPPORT = 1