diff --git a/mozilla/Makefile.in b/mozilla/Makefile.in
index ad37400f751..b54245a16b3 100644
--- a/mozilla/Makefile.in
+++ b/mozilla/Makefile.in
@@ -199,7 +199,7 @@ ifneq (,$(filter mac cocoa,$(MOZ_WIDGET_TOOLKIT)))
 tier_9_dirs	+= xpfe/bootstrap/appleevents
 endif
 
-ifdef THUNDERBIRD
+ifdef MOZ_THUNDERBIRD
 ifdef MOZ_USE_OFFICIAL_BRANDING
 tier_9_dirs  += other-licenses/branding/thunderbird
 endif