diff --git a/contrib/oid2name/oid2name.c b/contrib/oid2name/oid2name.c
index dbb3312a48..565baea1b6 100644
--- a/contrib/oid2name/oid2name.c
+++ b/contrib/oid2name/oid2name.c
@@ -7,6 +7,7 @@
  */
 
 #include <stdlib.h>
+#include <unistd.h>
 #include <string.h>
 
 #include "libpq-fe.h"