diff -r c13fb323b2fb -r 0d55cbe2e63e make/lib/Awt2dLibraries.gmk
--- a/make/lib/Awt2dLibraries.gmk	Fri May 04 10:09:27 2018 +0200
+++ b/make/lib/Awt2dLibraries.gmk	Fri May 04 10:55:57 2018 +0200
@@ -772,6 +772,17 @@
 
   ifeq ($(USE_EXTERNAL_LIBPNG), false)
     LIBSPLASHSCREEN_HEADER_DIRS += libsplashscreen/libpng
+
+    ifeq ($(OPENJDK_TARGET_OS), macosx)
+      ifeq ($(USE_EXTERNAL_LIBZ), true)
+        # When building our own libpng and using an external libz, we need to
+        # inject our own libz.h to tweak the exported ZLIB_VERNUM macro. See
+        # $(TOPDIR)/src/java.desktop/macosx/native/libsplashscreen/libpng/zlibwrapper/zlib.h
+        # for details. This must be specified with -iquote, not -I to avoid a
+        # circular include.
+        LIBSPLASHSCREEN_CFLAGS += -iquote $(TOPDIR)/src/$(MODULE)/macosx/native/libsplashscreen/libpng/zlibwrapper
+      endif
+    endif
   else
     LIBSPLASHSCREEN_EXCLUDES += libpng
   endif
@@ -804,18 +815,6 @@
     LIBSPLASHSCREEN_CFLAGS += -DWITH_X11 $(X_CFLAGS)
   endif
 
-  ifeq ($(USE_EXTERNAL_LIBZ), true)
-    ifeq ($(OPENJDK_TARGET_OS), macosx)
-      ifeq ($(USE_EXTERNAL_LIBPNG), false)
-        # When building our own libpng and using an external libz, we need to
-        # inject our own libz.h to tweak the exported ZLIB_VERNUM macro. See
-        # $(TOPDIR)/src/java.desktop/macosx/native/libsplashscreen/libpng/zlib.h
-        # for details.
-        LIBSPLASHSCREEN_CFLAGS += -iquote $(TOPDIR)/src/$(MODULE)/macosx/native/libsplashscreen/libpng
-      endif
-    endif
-  endif
-
   LIBSPLASHSCREEN_LIBS :=
 
   ifeq ($(OPENJDK_TARGET_OS), macosx)
@@ -844,7 +843,7 @@
       EXCLUDE_FILES := imageioJPEG.c jpegdecoder.c pngtest.c, \
       EXCLUDES := $(LIBSPLASHSCREEN_EXCLUDES), \
       OPTIMIZATION := LOW, \
-      CFLAGS := $(LIBSPLASHSCREEN_CFLAGS) $(CFLAGS_JDKLIB) \
+      CFLAGS := $(CFLAGS_JDKLIB) $(LIBSPLASHSCREEN_CFLAGS) \
           $(GIFLIB_CFLAGS) $(LIBJPEG_CFLAGS) $(PNG_CFLAGS) $(LIBZ_CFLAGS), \
       EXTRA_HEADER_DIRS := $(LIBSPLASHSCREEN_HEADER_DIRS), \
       DISABLED_WARNINGS_gcc := sign-compare type-limits unused-result \