diff --git a/superset/viz.py b/superset/viz.py
index a9e3f93e4..8eb062048 100644
--- a/superset/viz.py
+++ b/superset/viz.py
@@ -1765,9 +1765,7 @@ class WorldMapViz(BaseViz):
         columns = ['country', 'm1', 'm2']
         if metric == secondary_metric:
             ndf = df[cols]
-            # df[metric] will be a DataFrame
-            # because there are duplicate column names
-            ndf['m1'] = df[metric].iloc[:, 0]
+            ndf['m1'] = df[metric]
             ndf['m2'] = ndf['m1']
         else:
             if secondary_metric: