diff --git a/layout/style/Makefile.in b/layout/style/Makefile.in
index 60542cfc133a..8446f1dba99a 100644
--- a/layout/style/Makefile.in
+++ b/layout/style/Makefile.in
@@ -18,6 +18,9 @@ endif
 MODULE		= layout
 LIBRARY_NAME	= gkstyle_s
 LIBXUL_LIBRARY	= 1
+ifndef _MSC_VER
+FAIL_ON_WARNINGS = 1
+endif # !_MSC_VER
 
 EXPORTS_NAMESPACES = mozilla/css mozilla/dom