diff --git a/Python/dup2.c b/Python/dup2.c
index ba7413a0ca7..2579afd443d 100644
--- a/Python/dup2.c
+++ b/Python/dup2.c
@@ -12,6 +12,7 @@
  */
 
 #include <fcntl.h>
+#include <unistd.h>
 
 #define BADEXIT -1