diff --git a/test/minigzip.c b/test/minigzip.c
index 7868c64dd..3f21b1abe 100644
--- a/test/minigzip.c
+++ b/test/minigzip.c
@@ -14,6 +14,8 @@
 
 /* @(#) $Id$ */
 
+#define _POSIX_SOURCE 1  /* This file needs POSIX for fdopen(). */
+
 #include "zbuild.h"
 #ifdef ZLIB_COMPAT
 # include "zlib.h"