diff --git a/src/Mod/Fem/femsolver/elmer/sifio.py b/src/Mod/Fem/femsolver/elmer/sifio.py
index ab88ac3198..ad65a38ad7 100644
--- a/src/Mod/Fem/femsolver/elmer/sifio.py
+++ b/src/Mod/Fem/femsolver/elmer/sifio.py
@@ -305,7 +305,7 @@ class _Writer(object):
         self._stream.write(_SECTION_DELIM)
 
     def _writeSectionBody(self, s):
-        for key in sorted(s):  # def keys() from class sifio.Section is called
+        for key in sorted(s.keys()):  # def keys() from class sifio.Section is called
             self._writeAttribute(key, s[key])
 
     def _writeAttribute(self, key, data):