diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index b758344f310..a946b0d4d7d 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -48,7 +48,7 @@ Data members:
 
 #include "osdefs.h"
 
-#if HAVE_UNISTD_H
+#ifdef HAVE_UNISTD_H
 #include <unistd.h>
 #endif