diff --git a/python/pyspark/sql/dataframe.py b/python/pyspark/sql/dataframe.py
index 0f3480c239187..e4171d6386f41 100644
--- a/python/pyspark/sql/dataframe.py
+++ b/python/pyspark/sql/dataframe.py
@@ -568,8 +568,7 @@ def join(self, other, on=None, how=None):
 
         if on is None or len(on) == 0:
             jdf = self._jdf.join(other._jdf)
-
-        if isinstance(on[0], basestring):
+        elif isinstance(on[0], basestring):
             jdf = self._jdf.join(other._jdf, self._jseq(on))
         else:
             assert isinstance(on[0], Column), "on should be Column or list of Column"