diff --git a/Modules/main.c b/Modules/main.c
index 2a8bbdeb8ff..c8b583a455d 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -33,6 +33,9 @@ PERFORMANCE OF THIS SOFTWARE.
 
 #include "Python.h"
 
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
 
 /* Interface to getopt(): */
 extern int optind;