diff --git a/mhcflurry/antigen_presentation/presentation_model.py b/mhcflurry/antigen_presentation/presentation_model.py
index 82abcdf394506153674277e238027fae7ffdd7c4..a24899de1a83d5112dd4b684b6dd9da1d071df87 100644
--- a/mhcflurry/antigen_presentation/presentation_model.py
+++ b/mhcflurry/antigen_presentation/presentation_model.py
@@ -334,7 +334,7 @@ class PresentationModel(object):
                 predictions = sub_model.predict(peptides_df)
                 print("Input '%s' generated %d predictions in %0.2f sec." % (
                     sub_model, len(peptides_df), (time.time() - start_t)))
-                for (col, values) in predictions.items():
+                for (col, values) in predictions.iteritems():
                     values = pandas.Series(values)
                     assert_no_null(values)
                     df[col] = values