diff --git a/mozilla/config/rules.mk b/mozilla/config/rules.mk
index cc099ac442b..dbe94164546 100644
--- a/mozilla/config/rules.mk
+++ b/mozilla/config/rules.mk
@@ -210,7 +210,7 @@ endif # LIBRARY_NAME
 endif # MOZ_MAPINFO
 
 ifdef DEFFILE
-OS_LDFLAGS += /DEF:$(DEFFILE)
+OS_LDFLAGS += /DEF:$(DEFFILE)
 DSO_LDOPTS += /DEF:$(DEFFILE)
 endif