diff --git a/lib/spack/spack/cmd/flake8.py b/lib/spack/spack/cmd/flake8.py
index 9691ed138ba..c3a5d70e58a 100644
--- a/lib/spack/spack/cmd/flake8.py
+++ b/lib/spack/spack/cmd/flake8.py
@@ -79,9 +79,9 @@
 
     # exemptions applied to all files.
     r'.py$': {
-        # Exempt lines with URLs from overlong line errors.
         'E501': [
-            r'(https?|ftp|file)\:',
+            r'(https?|ftp|file)\:',        # URLs
+            r'([\'"])[0-9a-fA-F]{32,}\1',  # long hex checksums
         ]
     },
 }