diff --git a/mhcflurry/antigen_presentation/presentation_model.py b/mhcflurry/antigen_presentation/presentation_model.py
index f538ac2e77b9ea8ce479ea82a999b9424a3385d3..82abcdf394506153674277e238027fae7ffdd7c4 100644
--- a/mhcflurry/antigen_presentation/presentation_model.py
+++ b/mhcflurry/antigen_presentation/presentation_model.py
@@ -265,7 +265,7 @@ class PresentationModel(object):
 
         for sub_model in component_models:
             predictions = sub_model.predict(hits_and_decoys_df)
-            for (col, values) in predictions.items():
+            for (col, values) in predictions.iteritems():
                 hits_and_decoys_df[col] = values
 
         (x, y) = self.make_features_and_target(hits_and_decoys_df)