diff --git a/contrib/xml2/Makefile b/contrib/xml2/Makefile
index 0bd5b032976..e9ed20f128c 100644
--- a/contrib/xml2/Makefile
+++ b/contrib/xml2/Makefile
@@ -12,7 +12,7 @@ DATA_built = pgxml.sql
 DATA = uninstall_pgxml.sql
 DOCS = README.xml2
 
-override CFLAGS += $(shell xml2-config --cflags)
+PG_CPPFLAGS := $(shell xml2-config --cflags)
 
 ifdef USE_PGXS
 PGXS := $(shell pg_config --pgxs)