diff --git a/pygal/test/test_graph.py b/pygal/test/test_graph.py
index 0040526..77df284 100644
--- a/pygal/test/test_graph.py
+++ b/pygal/test/test_graph.py
@@ -20,6 +20,7 @@ import os
 import pygal
 import uuid
 import sys
+from pygal import i18n
 from pygal.util import cut
 from pygal._compat import u
 from pygal.test import pytest_generate_tests, make_data
@@ -69,6 +70,8 @@ def test_metadata(Chart):
     v = range(7)
     if Chart == pygal.XY:
         v = list(map(lambda x: (x, x + 1), v))
+    elif Chart == pygal.Worldmap:
+        v = list(map(lambda x: x, i18n.COUNTRIES))
 
     chart.add('Serie with metadata', [
         v[0],
diff --git a/pygal/util.py b/pygal/util.py
index d2cc7b1..8ab6958 100644
--- a/pygal/util.py
+++ b/pygal/util.py
@@ -346,6 +346,7 @@ def prepare_values(raw, config, cls):
                     (width - len(raw_values)) * [None]  # aligning values
                     if len(raw_values) < width else [])):
             if isinstance(raw_value, dict):
+                raw_value = dict(raw_value)
                 value = raw_value.pop('value', None)
                 metadata[index] = raw_value
             else: