diff --git a/Orange/widgets/visualize/owboxplot.py b/Orange/widgets/visualize/owboxplot.py
index 5811d0244e9..d0a9dd5b22e 100644
--- a/Orange/widgets/visualize/owboxplot.py
+++ b/Orange/widgets/visualize/owboxplot.py
@@ -494,12 +494,13 @@ def compute_box_data(self):
             self.dist = []
             self.conts = contingency.get_contingency(
                 dataset, attr, self.group_var)
+            group_var_labels = self.group_var.values + ["Missing value"]
             if self.is_continuous:
                 stats, label_texts = [], []
-                for i, cont in enumerate(self.conts):
+                for i, cont in enumerate(self.conts.array_with_unknowns):
                     if np.sum(cont[1]):
                         stats.append(BoxData(cont, attr, i, self.group_var))
-                        label_texts.append(self.group_var.values[i])
+                        label_texts.append(group_var_labels[i])
                 self.stats = stats
                 self.label_txts_all = label_texts
             else: