diff --git a/src/cryptlib/asn.cpp b/src/cryptlib/asn.cpp
index f5e7989..a0eb77a 100644
--- a/src/cryptlib/asn.cpp
+++ b/src/cryptlib/asn.cpp
@@ -3,6 +3,7 @@
 #include "pch.h"
 #include "asn.h"
 #include "misc.h"
+#include <stdlib.h>
 
 unsigned int DERLengthEncode(unsigned int length, byte *output)
 {