diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 483da03c47..fb5ea5d02b 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -1506,7 +1506,8 @@ def _cmp_key(self):
           2. The hash of each of this node's dependencies' cmp_keys.
         """
         return self._cmp_node() + (
-            tuple(sorted(hash(d) for d in self.dependencies.values())),)
+            tuple(hash(self.dependencies[name])
+                  for name in sorted(self.dependencies)),)
 
 
     def colorized(self):