diff --git a/python/pyspark/sql/functions.py b/python/pyspark/sql/functions.py
index 3860076dd8f2c..03266138024cd 100644
--- a/python/pyspark/sql/functions.py
+++ b/python/pyspark/sql/functions.py
@@ -82,7 +82,7 @@ def _create_binary_mathfunction(name, doc=""):
     def _(col1, col2):
         sc = SparkContext._active_spark_context
         # For legacy reasons, the arguments here can be implicitly converted into floats,
-        # if they are not columns.
+        # if they are not columns or strings.
         if isinstance(col1, Column):
             arg1 = col1._jc
         elif isinstance(col1, basestring):
diff --git a/python/pyspark/sql/tests/test_functions.py b/python/pyspark/sql/tests/test_functions.py
index aab82534acaa0..b77757342843d 100644
--- a/python/pyspark/sql/tests/test_functions.py
+++ b/python/pyspark/sql/tests/test_functions.py
@@ -158,7 +158,7 @@ def test_rand_functions(self):
 
     def test_string_functions(self):
         from pyspark.sql import functions
-        from pyspark.sql.functions import col, lit, upper, _string_functions
+        from pyspark.sql.functions import col, lit, _string_functions
         df = self.spark.createDataFrame([['nick']], schema=['name'])
         self.assertRaisesRegexp(
             TypeError,