diff --git a/Crypto/src/CryptoException.cpp b/Crypto/src/CryptoException.cpp
index c6496a197..b9770bb71 100644
--- a/Crypto/src/CryptoException.cpp
+++ b/Crypto/src/CryptoException.cpp
@@ -87,7 +87,7 @@ Poco::Exception* OpenSSLException::clone() const
 
 void OpenSSLException::setExtMessage()
 {
-	unsigned long e = ERR_get_error();
+	Poco::UInt64 e = static_cast<Poco::UInt64>(ERR_get_error());
 	char buf[128] = { 0 };
 	char* pErr = ERR_error_string(e, buf);
 	std::string err;