diff --git a/comut/comut.py b/comut/comut.py
index 270656c..3fca1de 100644
--- a/comut/comut.py
+++ b/comut/comut.py
@@ -1042,7 +1042,7 @@ def _plot_indicator_data(self, ax, data, name, plot_kwargs):
         for i, group in enumerate(set(data['group'])):
 
             # ignore missing samples
-            if np.isnan(group):
+            if df.isna(group):
                 continue
 
             # plot the first with a label so legend can extract it later