diff --git a/scd/app.c b/scd/app.c
index 21230bd30..c6bfd3f51 100644
--- a/scd/app.c
+++ b/scd/app.c
@@ -22,6 +22,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 #include <npth.h>
 
 #ifndef HAVE_W32_SYSTEM