How to get MethodInfo of interface method, having implementing MethodInfo of class method?

OK, I found a way, using GetInterfaceMap.

var map = targetType.GetInterfaceMap(interfaceMethod.DeclaringType);
var index = Array.IndexOf(map.InterfaceMethods, interfaceMethod);

if (index == -1)
{
    //this should literally be impossible
}

return map.TargetMethods[index];