Conversion doesn't work when I explicitly write it

I have 2 classes, each can be converted into other. When I just write for example a = b it compiles and converts as expected but when I do for example a = (OtherClass)b it throws me C2440 compile error. Anyone has idea why this happens?

This is what C2440 error says: "retyping: can't convert from Kelvin to Celsius"(and then "from Celsius to Kelvin")

#define ValueOperator(VALUETYPE) operator VALUETYPE() const { return this->value; }

using Value = double;

//this is in separated file
class Celsius;
class Kelvin
{
public:
    Value value;
    ValueOperator(Value);

    Kelvin();
    Kelvin(Value value);

    operator Celsius() const;
};

//this is in separated file
class Kelvin;
class Celsius
{
public:
    Value value;
    ValueOperator(Value);

    Celsius();
    Celsius(Value value);

    operator Kelvin() const;
};

int main()
{
    Celsius c = 50;
    Kelvin k = 10;

    c = k; //converts value as excepted
    c = (Celsius)k; //error C2440

    k = c; //converts value as excepted
    k = (Kelvin)c; //error C2440

    return 0;
}