diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index ebcc17a..f9a50ad 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -3,7 +3,7 @@
 If you want to add code, please make sure it passes the clang-format style (I'm using LLVM 4.0):
 
 ```bash
-git ls-files | grep -E '.cpp|.hpp' | xargs clang-format -i -style=file
+git ls-files -- '.cpp' '.hpp' | xargs clang-format -i -style=file
 ```
 
 It is also a good idea to check this with `clang-tidy`; automatic fixes can be made using `-DCLANG_TIDY_FIX-ON` (resets to `OFF` when rerunning CMake).