diff --git a/contrib/xml2/Makefile b/contrib/xml2/Makefile
index a7398c1a21..15187eacd1 100644
--- a/contrib/xml2/Makefile
+++ b/contrib/xml2/Makefile
@@ -11,7 +11,7 @@ SHLIB_LINK = -lxslt -lxml2
 DATA_built = 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)