diff --git a/config/config.initialize.m b/config/config.initialize.m
index 8889a94f0..bc103ae26 100644
--- a/config/config.initialize.m
+++ b/config/config.initialize.m
@@ -4,6 +4,10 @@
 #include "objc-common.g"
 #include <stdio.h>
 
+#if !defined(_MSC_VER)
+#include <unistd.h>
+#endif
+
 #if defined(_WIN32)
 
 #include <process.h>