--- a/make/lib/Lib-java.prefs.gmk	Thu Apr 12 14:11:59 2018 +0200
+++ b/make/lib/Lib-java.prefs.gmk	Mon Apr 16 11:48:41 2018 +0200
@@ -27,6 +27,7 @@
 
 ################################################################################
 
+# libprefs on macosx do not use the unix code, so we need to specify this explicitly.
 ifeq ($(OPENJDK_TARGET_OS), macosx)
   LIBPREF_SRC_DIRS := $(TOPDIR)/src/java.prefs/macosx/native/libprefs
 else
@@ -37,8 +38,8 @@
     NAME := prefs, \
     SRC := $(LIBPREF_SRC_DIRS), \
     OPTIMIZATION := HIGH, \
-    CFLAGS := $(CFLAGS_JDKLIB) $(addprefix -I, $(LIBPREF_SRC_DIRS)) \
-        $(LIBJAVA_HEADER_FLAGS), \
+    CFLAGS := $(CFLAGS_JDKLIB), \
+    HEADER_FLAGS := $(LIBJAVA_HEADER_FLAGS), \
     LDFLAGS := $(LDFLAGS_JDKLIB) \
         $(call SET_SHARED_LIBRARY_ORIGIN), \
     LIBS_unix := -ljvm, \