--- a/make/gensrc/GensrcCLDR.gmk	Tue Feb 05 10:24:39 2019 +0100
+++ b/make/gensrc/GensrcCLDR.gmk	Tue Feb 05 14:57:24 2019 +0100
@@ -40,7 +40,7 @@
 # tzmappings generation for Windows.
 # Since the rule is shared with CLDR_BASEMETAINFO_FILE target, note that
 # just removing the target tzmappings will not recreate the tzmappings file.
-ifeq ($(OPENJDK_TARGET_OS), windows)
+ifeq ($(call isTargetOs, windows), true)
   CLDR_WINTZMAPPINGS := $(GENSRC_BASEDIR)/windows/conf/tzmappings
   $(CLDR_WINTZMAPPINGS): $(CLDR_BASEMETAINFO_FILE)
 endif