diff --git a/Orange/widgets/unsupervised/owhierarchicalclustering.py b/Orange/widgets/unsupervised/owhierarchicalclustering.py
index dd73e5a708..e45228e874 100644
--- a/Orange/widgets/unsupervised/owhierarchicalclustering.py
+++ b/Orange/widgets/unsupervised/owhierarchicalclustering.py
@@ -149,7 +149,10 @@ def data(self, index, role=Qt.DisplayRole):
             return font
         if role == Qt.BackgroundRole:
             if self.__colors is not None:
-                return self.__colors[index.row()]
+                if index.row() < len(self.__colors):
+                    return self.__colors[index.row()]
+                else:
+                    return QColor()
             elif not any(self) and self.subset:  # no labels, no color, but subset
                 return QColor(0, 0, 0)
         if role == Qt.UserRole and self.subset:
diff --git a/Orange/widgets/unsupervised/tests/test_owhierarchicalclustering.py b/Orange/widgets/unsupervised/tests/test_owhierarchicalclustering.py
index baca8198ed..04afb193e9 100644
--- a/Orange/widgets/unsupervised/tests/test_owhierarchicalclustering.py
+++ b/Orange/widgets/unsupervised/tests/test_owhierarchicalclustering.py
@@ -1,10 +1,12 @@
 # Test methods with long descriptive names can omit docstrings
 # pylint: disable=missing-docstring, protected-access
+import unittest
 import warnings
 
 import numpy as np
 
 from AnyQt.QtCore import QPoint, Qt
+from AnyQt.QtGui import QColor
 from AnyQt.QtTest import QTest
 
 import Orange.misc
@@ -13,7 +15,7 @@
 from Orange.misc import DistMatrix
 from Orange.widgets.tests.base import WidgetTest, WidgetOutputsTestMixin
 from Orange.widgets.unsupervised.owhierarchicalclustering import \
-    OWHierarchicalClustering
+    OWHierarchicalClustering, SelectedLabelsModel
 
 
 class TestOWHierarchicalClustering(WidgetTest, WidgetOutputsTestMixin):
@@ -226,3 +228,16 @@ def test_many_values_warning(self):
 
         self.send_signal(self.widget.Inputs.distances, None)
         self.assertFalse(w.Warning.many_clusters.is_shown())
+
+
+class TestSelectedLabelsModel(unittest.TestCase):
+    def test_model_extend(self):
+        model = SelectedLabelsModel()
+        model[:] = ["1"]
+        model.set_colors([QColor(Qt.blue)])
+        index = model.index(0)
+        self.assertEqual(index.data(Qt.DisplayRole), "1")
+        self.assertEqual(index.data(Qt.BackgroundRole), QColor(Qt.blue))
+        model[:]= ["1", "2"]
+        index1 = model.index(1)
+        self.assertEqual(index1.data(Qt.BackgroundRole), QColor()) # should be invalid color