Test it.

spec/babel-spec.coffee

@@ -36,6 +36,11 @@ describe "Babel transpiler support", ->
       transpiled = require('./fixtures/babel/babel-double-quotes.js')
       expect(transpiled(3)).toBe 4
 
+  describe 'when a .js file starts with /* @flow */', ->
+    it "transpiles it using babel", ->
+      transpiled = require('./fixtures/babel/flow-comment.js')
+      expect(transpiled(3)).toBe 4
+
   describe "when a .js file does not start with 'use babel';", ->
     it "does not transpile it using babel", ->
       expect(-> require('./fixtures/babel/invalid.js')).toThrow()

spec/fixtures/babel/flow-comment.js

@@ -0,0 +1,4 @@
+/* @flow */
+
+const f: Function = v => v + 1
+module.exports = f