diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 9e89feb1483..c757e6b0d6f 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -3395,7 +3395,8 @@ def __init__(self, spec, hash):
 class NoSuchHashError(SpecError):
     def __init__(self, hash):
         super(NoSuchHashError, self).__init__(
-            "No installed spec matches the hash: '%s'")
+            "No installed spec matches the hash: '%s'"
+            % hash)
 
 
 class RedundantSpecError(SpecError):