--- a/toolkit/locales/l10n.mk
+++ b/toolkit/locales/l10n.mk
@@ -187,17 +187,17 @@ merge-%:
 # from l10n-central.
 ifdef NIGHTLY_BUILD
 	@if  ! test -d $(L10NBASEDIR)/$(AB_CD) ; then \
 		$(NSINSTALL) -D $(L10NBASEDIR) ; \
 		$(L10N_CO) ; \
 	fi
 endif
 	$(RM) -rf $(REAL_LOCALE_MERGEDIR)
-	-$(MOZILLA_DIR)/mach compare-locales --merge $(BASE_MERGE) $(srcdir)/l10n.toml $(L10NBASEDIR) $*
+	-$(MOZILLA_DIR)/mach compare-locales $(COMPARE_LOCALES_DEFINES) --merge $(BASE_MERGE) $(srcdir)/l10n.toml $(L10NBASEDIR) $*
 
 langpack-%: IS_LANGUAGE_REPACK=1
 langpack-%: IS_LANGPACK=1
 langpack-%: AB_CD=$*
 langpack-%:
 	@echo 'Making langpack $(LANGPACK_FILE)'
 	@$(MAKE) libs-$(AB_CD)
 	@$(MAKE) package-langpack-$(AB_CD)