diff --git a/edify/expr.h b/edify/expr.h
index 1462531..8e1c638 100644
--- a/edify/expr.h
+++ b/edify/expr.h
@@ -17,6 +17,8 @@
 #ifndef _EXPRESSION_H
 #define _EXPRESSION_H
 
+#include <unistd.h>
+
 #include "yydefs.h"
 
 #define MAX_STRING_LEN 1024