diff --git a/lib/spack/spack/cmd/flake8.py b/lib/spack/spack/cmd/flake8.py
index a6dc941190d..546a27c7658 100644
--- a/lib/spack/spack/cmd/flake8.py
+++ b/lib/spack/spack/cmd/flake8.py
@@ -88,7 +88,7 @@ def changed_files():
 
     git_args = [
         # Add changed files committed since branching off of develop
-        ['diff', '--name-only', '--diff-filter=ACMR', 'develop'],
+        ['diff', '--name-only', '--diff-filter=ACMR', 'develop...'],
         # Add changed files that have been staged but not yet committed
         ['diff', '--name-only', '--diff-filter=ACMR', '--cached'],
         # Add changed files that are unstaged