diff --git a/ports/unix/moduos.c b/ports/unix/moduos.c
index 848a3612d1..b577dbd297 100644
--- a/ports/unix/moduos.c
+++ b/ports/unix/moduos.c
@@ -25,6 +25,7 @@
  * THE SOFTWARE.
  */
 
+#include <errno.h>
 #include <stdlib.h>
 #include <string.h>