diff --git a/Foundation/include/Poco/Dynamic/Struct.h b/Foundation/include/Poco/Dynamic/Struct.h
index 1f948d647..ebd6a5f47 100644
--- a/Foundation/include/Poco/Dynamic/Struct.h
+++ b/Foundation/include/Poco/Dynamic/Struct.h
@@ -530,12 +530,12 @@ public:
 		return false;
 	}
 
-	Var& operator [] (std::size_t name)
+	Var& operator [] (int name)
 	{
 		return _val[name];
 	}
 
-	const Var& operator [] (std::size_t name) const
+	const Var& operator [] (int name) const
 	{
 		return _val[name];
 	}
diff --git a/Foundation/include/Poco/Dynamic/Var.h b/Foundation/include/Poco/Dynamic/Var.h
index 290df9076..078cb74e7 100644
--- a/Foundation/include/Poco/Dynamic/Var.h
+++ b/Foundation/include/Poco/Dynamic/Var.h
@@ -436,7 +436,7 @@ public:
 				InvalidAccessException>("Not an array.")->operator[](n);
 		else if (isStruct())
 			return structIndexOperator(holderImpl<Struct<int>,
-				InvalidAccessException>("Not a struct."), n);
+				InvalidAccessException>("Not a struct."), static_cast<int>(n));
 		else
 			throw InvalidAccessException("Must be struct or array.");
 	}
@@ -451,7 +451,7 @@ public:
 				InvalidAccessException>("Not an array.")->operator[](n);
 		else if (isStruct())
 			return structIndexOperator(holderImpl<Struct<int>,
-				InvalidAccessException>("Not a struct."), n);
+				InvalidAccessException>("Not a struct."), static_cast<int>(n));
 		else
 			throw InvalidAccessException("Must be struct or array.");
 	}