diff --git a/lib/spack/spack/concretize.py b/lib/spack/spack/concretize.py
index fb8dfb3ee47..801d3f162a3 100644
--- a/lib/spack/spack/concretize.py
+++ b/lib/spack/spack/concretize.py
@@ -183,6 +183,8 @@ def concretize_compiler_flags(self, spec):
         """
         ret = False
         for flag in Compiler.valid_compiler_flags():
+            if flag in spec.compiler_flags:
+                continue
             try:
                 nearest = next(p for p in spec.traverse(direction='parents')
                                if ((p.compiler == spec.compiler and p is not spec)
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 72117e1cb3f..406bb6aa436 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -1745,7 +1745,7 @@ def tree(self, **kwargs):
         showid = kwargs.pop('ids',   False)
         cover  = kwargs.pop('cover', 'nodes')
         indent = kwargs.pop('indent', 0)
-        fmt    = kwargs.pop('format', '$_$@$%@$+$+arch=')
+        fmt    = kwargs.pop('format', '$_$@$%@+$+$=')
         prefix = kwargs.pop('prefix', None)
         check_kwargs(kwargs, self.tree)