diff --git a/lib/spack/spack/architecture.py b/lib/spack/spack/architecture.py
index 4485bbe8401..cbac7b41d65 100644
--- a/lib/spack/spack/architecture.py
+++ b/lib/spack/spack/architecture.py
@@ -424,8 +424,7 @@ def _operating_system_from_dict(os_name, platform=None):
     """
     if not platform:
         platform = sys_type()
-    if isinstance(os_name, spack.util.spack_yaml.syaml_dict) or \
-            isinstance(os_name, dict):
+    if isinstance(os_name, dict):
         name = os_name['name']
         version = os_name['version']
         return platform.operating_system(name+version)