diff --git a/extensions/gio/Makefile.in b/extensions/gio/Makefile.in
index 79112a848eb2..1e29ec64f3d5 100644
--- a/extensions/gio/Makefile.in
+++ b/extensions/gio/Makefile.in
@@ -17,6 +17,7 @@ IS_COMPONENT	= 1
 EXPORT_LIBRARY	= 1
 MODULE_NAME	= nsGIOModule
 LIBXUL_LIBRARY	= 1
+FAIL_ON_WARNINGS = 1
 
 CPPSRCS		= \
 		nsGIOProtocolHandler.cpp \
diff --git a/toolkit/system/gnome/Makefile.in b/toolkit/system/gnome/Makefile.in
index 4b96165e3fbc..0f18c2a35f9d 100644
--- a/toolkit/system/gnome/Makefile.in
+++ b/toolkit/system/gnome/Makefile.in
@@ -13,6 +13,7 @@ MODULE		= mozgnome
 LIBRARY_NAME	= mozgnome
 FORCE_SHARED_LIB = 1
 IS_COMPONENT	= 1
+FAIL_ON_WARNINGS = 1
 
 
 CPPSRCS = \