diff --git a/mhcflurry/plotting.py b/mhcflurry/plotting.py
index 6be12a41679a1c6ec90ee08d49d44bb3c9c182b0..c1ce28ca4894d62d22ce986762965a6a55876f72 100644
--- a/mhcflurry/plotting.py
+++ b/mhcflurry/plotting.py
@@ -34,7 +34,7 @@ def plot_nsamples_vs_metrics_with_imputation(
     seaborn.set_style("whitegrid")
 
     for (j, score_name) in enumerate(metrics):
-        ax = pyplot.subplot2grid((1, 4), (0, j))
+        pyplot.subplot2grid((1, 4), (0, j))
         groups = results_df.groupby(groupby_columns)
         groups_score = groups[score_name].mean().to_frame().reset_index()
         groups_score["std_error"] = \
diff --git a/script/create-combined-class1-dataset.py b/script/create-combined-class1-dataset.py
index b75fbca603294db6c134d61288f84cf7da36d312..e51b46012ddfd1796527378bce5284fb3369e91d 100755
--- a/script/create-combined-class1-dataset.py
+++ b/script/create-combined-class1-dataset.py
@@ -171,7 +171,7 @@ if __name__ == "__main__":
 
     # filter out post-translation modifications and peptides with unknown
     # residues
-    modified_peptide_mask = combined_df.peptide.str.contains("+")
+    modified_peptide_mask = combined_df.peptide.str.contains("\+")
     n_modified = modified_peptide_mask.sum()
     if n_modified > 0:
         print("Dropping %d modified peptides" % n_modified)