diff --git a/lib/spack/spack/cmd/create.py b/lib/spack/spack/cmd/create.py
index 71bd196598..f5f234d7a7 100644
--- a/lib/spack/spack/cmd/create.py
+++ b/lib/spack/spack/cmd/create.py
@@ -145,7 +145,8 @@ def __call__(self, stage):
             'cmake':     "depends_on('cmake')",
             'scons':     "depends_on('scons')",
             'python':    "extends('python')",
-            'R':         "extends('R')"
+            'R':         "extends('R')",
+            'unknown':   "# depends_on('foo')"
         }
 
         # Default installation instructions