diff --git a/src/Mod/Idf/Idf.py b/src/Mod/Idf/Idf.py
index 507a616197..dc847eb0f0 100644
--- a/src/Mod/Idf/Idf.py
+++ b/src/Mod/Idf/Idf.py
@@ -22,11 +22,15 @@
 #*   Milos Koutny 2010                                                     *
 #***************************************************************************/
 
-import FreeCAD, Part, os, FreeCADGui, __builtin__
+import FreeCAD, Part, os, FreeCADGui
 from FreeCAD import Base
 from math import *
 import ImportGui
 
+# to distinguish python built-in open function from the one declared here
+if open.__module__ in ['__builtin__','io']:
+    pythonopen = open
+
 ##########################################################
 # Script version dated 19-Jan-2012                       #
 ##########################################################
@@ -54,8 +58,6 @@ IDF_diag_path="/tmp" # path for output of footprint.lst and missing_models.lst
 #              End config section do not touch code below                              #
 ########################################################################################
 
-pythonopen = __builtin__.open # to distinguish python built-in open function from the one declared here
-
 def open(filename):
 	"""called when freecad opens an Emn file"""
 	docname = os.path.splitext(os.path.basename(filename))[0]