diff --git a/src/backend/utils/mmgr/mcxt.c b/src/backend/utils/mmgr/mcxt.c
index 7acd9c02a728f0b6682add8aabe7a5c6d4d6aabe..2fad06c36fe18fca6cd642036323be306f1f89c3 100644
--- a/src/backend/utils/mmgr/mcxt.c
+++ b/src/backend/utils/mmgr/mcxt.c
@@ -19,11 +19,11 @@
  *-------------------------------------------------------------------------
  */
 
-#include "postgres.h"
-
-/* see palloc.h */
+/* see palloc.h.  Must be before postgres.h */
 #define MCXT_INCLUDE_DEFINITIONS
 
+#include "postgres.h"
+
 #include "utils/memutils.h"