generalized IntMap - IntegerMap or IntegralMap

I want to use Word32 or Word64 bit patterns as indices for a Map. I have checked that IntMap is more efficient than Map in my application. However, the Haskell 98 report warrants only 30 bits for Int including the sign bit. Is there a generalization of IntMap for Map Integer or (Integral k, Bits k) => Map k or would there be general interest in such a data structure?