diff --git a/Foundation/include/Poco/Dynamic/VarHolder.h b/Foundation/include/Poco/Dynamic/VarHolder.h
index 0f9cb4910..2116868b8 100644
--- a/Foundation/include/Poco/Dynamic/VarHolder.h
+++ b/Foundation/include/Poco/Dynamic/VarHolder.h
@@ -398,20 +398,36 @@ protected:
 
 private:
 
-	template <typename F, typename T>
-	void POCO_UNUSED checkUpperLimit(const F& from) const
-	{
-		if ((sizeof(T) < sizeof(F)) &&
-			(from > static_cast<F>(std::numeric_limits<T>::max())))
+		template <typename F, typename T>
+		void POCO_UNUSED checkUpperLimit(const F& from) const
 		{
-			throw RangeException("Value too large.");
+			// casting to type of smaller size AND
+			// 'from' is greater than 'T' max value
+			if ((sizeof(T) < sizeof(F)) &&
+				(from > static_cast<F>(std::numeric_limits<T>::max())))
+			{
+				throw RangeException("Value too large.");
+			}
+			// casting to type of equal/bigger size AND
+			// 'F' is signed AND
+			// 'T' is unsigned AND
+			// 'from' is negative
+			else if (std::numeric_limits<F>::is_signed &&
+					!std::numeric_limits<T>::is_signed && from < 0)
+			{
+				throw RangeException("Value too small.");
+			}
+			// casting to type of equal/bigger size AND
+			// 'F' is unsigned AND
+			// 'T' is signed AND
+			// 'from' is greater than 'T' max value
+			else if (!std::numeric_limits<F>::is_signed &&
+					  std::numeric_limits<T>::is_signed &&
+					  static_cast<Poco::UInt64>(from) > std::numeric_limits<T>::max())
+			{
+				throw RangeException("Value too large.");
+			}
 		}
-		else
-		if (from > std::numeric_limits<T>::max())
-		{
-			throw RangeException("Value too large.");
-		}
-	}
 
 
 	template <typename F, typename T>
diff --git a/Foundation/testsuite/src/CoreTest.cpp b/Foundation/testsuite/src/CoreTest.cpp
index b8a03ca93..ab96e10d3 100644
--- a/Foundation/testsuite/src/CoreTest.cpp
+++ b/Foundation/testsuite/src/CoreTest.cpp
@@ -79,9 +79,10 @@ namespace
 		{
 		}
 
-		NonDefaultConstructible operator=(int val)
+		NonDefaultConstructible& operator=(int val)
 		{
 			_val = val;
+			return *this;
 		}
 
 		bool operator == (const NonDefaultConstructible& other) const