diff --git a/mhcflurry/class1_affinity_prediction/class1_affinity_predictor.py b/mhcflurry/class1_affinity_prediction/class1_affinity_predictor.py
index c3b841da7bcb649a543cee22ced0e09d5c527f41..30f03ea1d0140bb60943dd97434196cbba986fa7 100644
--- a/mhcflurry/class1_affinity_prediction/class1_affinity_predictor.py
+++ b/mhcflurry/class1_affinity_prediction/class1_affinity_predictor.py
@@ -569,7 +569,6 @@ class Class1AffinityPredictor(object):
         for (allele, sub_df) in df.groupby("allele"):
             df.loc[sub_df.index, "result"] = self.percentile_ranks(
                 sub_df.affinity, allele=allele, throw=throw)
-        assert not df.result.isnull().any()
         return df.result.values
 
     def predict(self, peptides, alleles=None, allele=None, throw=True):