diff --git a/tests/test_repository_lib.py b/tests/test_repository_lib.py
index aecefb11..e754d70e 100755
--- a/tests/test_repository_lib.py
+++ b/tests/test_repository_lib.py
@@ -649,13 +649,25 @@ def test_sign_metadata(self):
     root_private_key = \
       repo_lib.import_rsa_privatekey_from_file(root_private_keypath, 'password')
     
+    # Sign with a valid, but not a threshold, key.
+    targets_private_keypath = os.path.join(keystore_path, 'targets_key')
+    targets_private_key = \
+      repo_lib.import_rsa_privatekey_from_file(targets_private_keypath,
+                                               'password')
+
     # sign_metadata() expects the private key 'root_metadata' to be in
     # 'tuf.keydb'.  Remove any public keys that may be loaded before
     # adding private key, otherwise a 'tuf.KeyAlreadyExists' exception is
     # raised.
     tuf.keydb.remove_key(root_private_key['keyid'])
     tuf.keydb.add_key(root_private_key)
-
+    tuf.keydb.remove_key(targets_private_key['keyid'])
+    tuf.keydb.add_key(targets_private_key)
+   
+    root_keyids.extend(tuf.roledb.get_role_keyids('targets'))
+    # Add the snapshot's public key (to test whether non-private keys are
+    # ignored by sign_metadata()).
+    root_keyids.extend(tuf.roledb.get_role_keyids('snapshot'))
     root_signable = repo_lib.sign_metadata(root_metadata, root_keyids,
                                            root_filename) 
     self.assertTrue(tuf.formats.SIGNABLE_SCHEMA.matches(root_signable))
@@ -669,7 +681,7 @@ def test_sign_metadata(self):
     self.assertRaises(tuf.FormatError, repo_lib.sign_metadata, root_metadata,
                       root_keyids, 3)
 
-    # Test 
+    # Test for a key that does not contain the private portion. 
 
 
 
diff --git a/tuf/repository_lib.py b/tuf/repository_lib.py
index ccf17122..5ee92038 100755
--- a/tuf/repository_lib.py
+++ b/tuf/repository_lib.py
@@ -1795,11 +1795,14 @@ def sign_metadata(metadata_object, keyids, filename):
     for signature in signable['signatures']:
       if not keyid == signature['keyid']:
         signatures.append(signature)
+      
+      else:
+        continue
     signable['signatures'] = signatures
 
     # Generate the signature using the appropriate signing method.
     if key['keytype'] in SUPPORTED_KEY_TYPES:
-      if len(key['keyval']['private']):
+      if 'private' in key['keyval']:
         signed = signable['signed']
         signature = tuf.keys.create_signature(key, signed)
         signable['signatures'].append(signature)