diff --git a/lib/spack/spack/packages.py b/lib/spack/spack/packages.py
index 9d87c3a94b..080644fb90 100644
--- a/lib/spack/spack/packages.py
+++ b/lib/spack/spack/packages.py
@@ -67,22 +67,22 @@ def get(self, spec, **kwargs):
         if spec.virtual:
             raise UnknownPackageError(spec.name)
 
-        dhash = spec.dag_hash()
+        key = hash(spec)
         if kwargs.get('new', False):
-            if dhash in self.instances:
-                del self.instances[dhash]
+            if key in self.instances:
+                del self.instances[key]
 
-        if not dhash in self.instances:
+        if not key in self.instances:
             package_class = self.get_class_for_package_name(spec.name)
             try:
                 copy = spec.copy() # defensive copy.  Package owns its spec.
-                self.instances[dhash] = package_class(copy)
+                self.instances[key] = package_class(copy)
             except Exception, e:
                 if spack.debug:
                     sys.excepthook(*sys.exc_info())
                 raise FailedConstructorError(spec.name, e)
 
-        return self.instances[dhash]
+        return self.instances[key]
 
 
     @_autospec
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index f62182ce76..483da03c47 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -1481,8 +1481,11 @@ def ne_dag(self, other):
 
     def _cmp_node(self):
         """Comparison key for just *this node* and not its deps."""
-        return (self.name, self.versions, self.variants,
-                self.architecture, self.compiler)
+        return (self.name,
+                self.versions,
+                self.variants,
+                self.architecture,
+                self.compiler)
 
 
     def eq_node(self, other):
@@ -1496,11 +1499,14 @@ def ne_node(self, other):
 
 
     def _cmp_key(self):
-        """Comparison key for this node and all dependencies *without*
-           considering structure.  This is the default, as
-           normalization will restore structure.
+        """This returns a key for the spec *including* DAG structure.
+
+        The key is the concatenation of:
+          1. A tuple describing this node in the DAG.
+          2. The hash of each of this node's dependencies' cmp_keys.
         """
-        return self._cmp_node() + (self.sorted_deps(),)
+        return self._cmp_node() + (
+            tuple(sorted(hash(d) for d in self.dependencies.values())),)
 
 
     def colorized(self):