diff --git a/var/spack/repos/builtin/packages/grep/package.py b/var/spack/repos/builtin/packages/grep/package.py
index 76f0b5f07061b1..40bd0deddb01b5 100644
--- a/var/spack/repos/builtin/packages/grep/package.py
+++ b/var/spack/repos/builtin/packages/grep/package.py
@@ -35,12 +35,16 @@ class Grep(AutotoolsPackage):
     @classmethod
     def determine_version(cls, exe):
         version_string = Executable(exe)("--version", output=str, error=str).split('\n')[0]
+        # Linux
         if "GNU grep" in version_string:
             return version_string.lstrip("grep (GNU grep)").strip()
+        # macOS
         elif "BSD grep, GNU compatible" in version_string:
-            return version_string.lstrip("grep (BSD grep, GNU compatible)").rstrip("-FreeBSD").strip()
+            return (
+                version_string.lstrip("grep (BSD grep, GNU compatible)").rstrip("-FreeBSD").strip()
+            )
+        # Don't know how to handle this version of grep, don't add it
         else:
-            # Don't know how to handle this version of grep, don't add it
             return None
 
     def configure_args(self):