diff --git a/pyomo/core/base/block.py b/pyomo/core/base/block.py
index 3c642427086..5063073bd12 100644
--- a/pyomo/core/base/block.py
+++ b/pyomo/core/base/block.py
@@ -1359,7 +1359,7 @@ def _component_data_iter(self, ctype=None, active=None, sort=False):
                 _items = ((None, comp),)
 
             if _sort_indices:
-                _items = sorted_robust(_items)
+                _items = sorted_robust(_items, key=itemgetter(0))
             if active is None or not isinstance(comp, ActiveIndexedComponent):
                 for idx, compData in _items:
                     yield (name, idx), compData
diff --git a/pyomo/core/tests/unit/test_block.py b/pyomo/core/tests/unit/test_block.py
index ac6710c9186..0fce0f14117 100644
--- a/pyomo/core/tests/unit/test_block.py
+++ b/pyomo/core/tests/unit/test_block.py
@@ -342,6 +342,15 @@ def test_Block(self):
         self.assertEqual(sorted([id(comp) for comp in model.block_data_objects(sort=False)]),
                          sorted([id(comp) for comp in [model,]+model.component_data_lists[Block]]))
 
+    def test_mixed_index_type(self):
+        m = ConcreteModel()
+        m.I = Set(initialize=[1,'1',3.5,4])
+        m.x = Var(m.I)
+        v = list(m.component_data_objects(Var, sort=True))
+        self.assertEqual(len(v), 4)
+        for a,b in zip([m.x[1], m.x[3.5], m.x[4], m.x['1']], v):
+            self.assertIs(a, b)
+
 
 class HierarchicalModel(object):
     def __init__(self):