--- core/SCsub.orig	2019-05-02 02:03:58 UTC
+++ core/SCsub
@@ -80,7 +80,7 @@ if env['builtin_zlib']:
 	]
 	thirdparty_zlib_sources = [thirdparty_zlib_dir + file for file in thirdparty_zlib_sources]
 
-	env_thirdparty.Append(CPPPATH=[thirdparty_zlib_dir])
+	env_thirdparty.Prepend(CPPPATH=[thirdparty_zlib_dir])
 	# Needs to be available in main env too
 	env.Append(CPPPATH=[thirdparty_zlib_dir])
 
@@ -128,7 +128,7 @@ if env['builtin_zstd']:
     ]
     thirdparty_zstd_sources = [thirdparty_zstd_dir + file for file in thirdparty_zstd_sources]
 
-    env_thirdparty.Append(CPPPATH=[thirdparty_zstd_dir, thirdparty_zstd_dir + "common"])
+    env_thirdparty.Prepend(CPPPATH=[thirdparty_zstd_dir, thirdparty_zstd_dir + "common"])
     env_thirdparty.Append(CCFLAGS="-DZSTD_STATIC_LINKING_ONLY")
     env.Append(CPPPATH=thirdparty_zstd_dir)
     # Also needed in main env includes will trigger warnings