diff --git a/xlwings/__init__.py b/xlwings/__init__.py
index b7525a9ec..e6cad0a49 100644
--- a/xlwings/__init__.py
+++ b/xlwings/__init__.py
@@ -15,7 +15,7 @@
     string_types = basestring
     xrange = xrange
     from future_builtins import map
-    import __builtins__ as builtins
+    builtins = __builtins__
 
 # Platform specifics
 if sys.platform.startswith('win'):
diff --git a/xlwings/_xlwindows.py b/xlwings/_xlwindows.py
index d52f980d2..f8720d814 100644
--- a/xlwings/_xlwindows.py
+++ b/xlwings/_xlwindows.py
@@ -406,6 +406,8 @@ def prepare_xl_data_element(x):
         return _datetime_to_com_time(x)
     elif np and isinstance(x, np.generic):
         return float(x)
+    elif x is None:
+        return ""
     else:
         return x
 
diff --git a/xlwings/tests/udfs/udf_tests.py b/xlwings/tests/udfs/udf_tests.py
index 70c52fef2..2a1866d4d 100644
--- a/xlwings/tests/udfs/udf_tests.py
+++ b/xlwings/tests/udfs/udf_tests.py
@@ -497,5 +497,11 @@ def optional_args(x, y=None):
         y = 10
     return x * y
 
+
+@xw.func
+def write_none():
+    return None
+
+
 if __name__ == "__main__":
     xw.serve()
diff --git a/xlwings/tests/udfs/udf_tests.xlsm b/xlwings/tests/udfs/udf_tests.xlsm
index a5c312351..1041957d9 100644
Binary files a/xlwings/tests/udfs/udf_tests.xlsm and b/xlwings/tests/udfs/udf_tests.xlsm differ