diff --git a/reactos/subsys/system/calc/winecalc.c b/reactos/subsys/system/calc/winecalc.c
index 9c563e14979..02028cb1ffd 100644
--- a/reactos/subsys/system/calc/winecalc.c
+++ b/reactos/subsys/system/calc/winecalc.c
@@ -20,6 +20,7 @@
 
 #include <stdio.h> // sprintf
 #include <math.h>
+#include <stdlib.h>
 
 #include <windows.h>
 #include <tchar.h>