**Search Terms:** source maps **Code** ```ts const fn = (arg) => { }; const fn2 = arg2 => { }; ``` **Expected behavior:** Source maps should both map the argument binding identifier to the location of the new binding. **Actual behavior:** The arrow that doesn't have parens maps the `arg2` binding to the whole function header. <img width="516" alt="screen shot 2018-03-21 at 5 30 45 pm" src="https://user-images.githubusercontent.com/132260/37847276-7dd70906-2e8d-11e8-83b1-6cbb04bcf4e5.png"> vs <img width="522" alt="screen shot 2018-03-21 at 5 30 34 pm" src="https://user-images.githubusercontent.com/132260/37847265-78059466-2e8d-11e8-8ab7-2976d8927ad9.png"> **Related Issues:** * #22833