``` var x = { 1234:"a", 5678:"b" } ``` Flow generates an error per integer key. According to [11.1.5 of ECMA-262](http://www.ecma-international.org/ecma-262/5.1/#sec-11.1.5) this is a perfectly valid construct. EDIT: @jgrund 's solution in https://github.com/facebook/flow/issues/380#issuecomment-224380551 works well