diff --git a/Crypto/include/Poco/Crypto/CryptoTransform.h b/Crypto/include/Poco/Crypto/CryptoTransform.h
index 1552c86cd..147bd2619 100644
--- a/Crypto/include/Poco/Crypto/CryptoTransform.h
+++ b/Crypto/include/Poco/Crypto/CryptoTransform.h
@@ -41,7 +41,7 @@
 
 
 #include "Poco/Crypto/Crypto.h"
-
+#include <fstream> // std::streamsize
 
 namespace Poco {
 namespace Crypto {