typedef enum type as key to NSDictionary?

Are enums not allowed as keys for an NSMutableDictionary?

When I try to add to the dictionary via:

[self.allControllers setObject:aController forKey:myKeyType];

I get the error:

error: incompatible type for argument 2 of 'setObject:forKey:'

Typically, I use NSString as my key name which doesn't require a cast to 'id' but to make the error go away, I had do that. Is the casting the correct behavior here or are enums as keys a bad idea?

My enum is defined as:

typedef enum tagMyKeyType
{
  firstItemType = 1,
  secondItemType = 2
} MyKeyType;

And the dictionary is defined and properly allocated as such:

NSMutableDictionary *allControllers;

allControllers = [[NSMutableDictionary alloc] init];