diff --git a/lib/spack/spack/test/package_sanity.py b/lib/spack/spack/test/package_sanity.py
index 3be74be7f88..5c18544a567 100644
--- a/lib/spack/spack/test/package_sanity.py
+++ b/lib/spack/spack/test/package_sanity.py
@@ -174,7 +174,7 @@ def invalid_sha256_digest(fetcher):
                 if bad_digest:
                     errors.append(
                         "All packages must use sha256 checksums."
-                        "Resource in %s uses %s." % (name, bad_digest)
+                        "Resource in %s uses %s." % (name,  bad_digest)
                     )
 
     assert [] == errors