diff --git a/lib/spack/spack/mirror.py b/lib/spack/spack/mirror.py
index 97aeef54347..aef5e2e8ee3 100644
--- a/lib/spack/spack/mirror.py
+++ b/lib/spack/spack/mirror.py
@@ -104,6 +104,9 @@ def get_matching_versions(specs, **kwargs):
                 s = Spec(pkg.name)
                 s.versions = VersionList([v])
                 s.variants = spec.variants.copy()
+                # This is needed to avoid hanging references during the
+                # concretization phase
+                s.variants.spec = s
                 matching_spec.append(s)
 
         if not matching_spec: