--- a/make/gendata/Gendata-jdk.compiler.gmk	Wed Sep 19 08:49:07 2018 +0100
+++ b/make/gendata/Gendata-jdk.compiler.gmk	Wed Sep 19 10:50:25 2018 +0200
@@ -42,7 +42,7 @@
 # Get the complete module source path:
 CT_MODULESOURCEPATH := $(call GetModuleSrcPath)
 
-CT_DATA_DESCRIPTION ?= $(TOPDIR)/make/data/symbols/symbols
+CT_DATA_DESCRIPTION += $(TOPDIR)/make/data/symbols/symbols
 
 COMPILECREATESYMBOLS_ADD_EXPORTS := \
     --add-exports jdk.compiler.interim/com.sun.tools.javac.api=ALL-UNNAMED \