--- old/make/gensrc/GensrcX11Wrappers.gmk	2020-03-23 19:56:34.327962719 +0100
+++ new/make/gensrc/GensrcX11Wrappers.gmk	2020-03-23 19:56:34.031962721 +0100
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2012, 2019, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2012, 2020, Oracle and/or its affiliates. All rights reserved.
 # DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 #
 # This code is free software; you can redistribute it and/or modify it
@@ -26,6 +26,9 @@
 # Generate java sources using the X11 offsets that are precalculated in files
 # make/data/x11wrappergen/sizes-<address size>.txt.
 
+TOOL_WRAPPERGENERATOR = $(JAVA_SMALL) -cp $(BUILDTOOLS_OUTPUTDIR)/jdk_tools_classes \
+    org.openjdk.buildtools.x11wrappergen.WrapperGenerator
+
 # Put the generated Java classes used to interface X11 from awt here.
 GENSRC_X11WRAPPERS_OUTPUTDIR := $(SUPPORT_OUTPUTDIR)/gensrc/java.desktop/sun/awt/X11