diff --git a/pandas/core/index.py b/pandas/core/index.py
index 8b650fea9b440..bd56bf9808eb9 100644
--- a/pandas/core/index.py
+++ b/pandas/core/index.py
@@ -2531,7 +2531,7 @@ def _evaluate_numeric_binop(self, other):
                 if reversed:
                     values, other = other, values
 
-                return self._shallow_copy(op(values, other))
+                return Index(op(values, other), **self._get_attributes_dict())
 
             return _evaluate_numeric_binop
 
diff --git a/pandas/tests/test_index.py b/pandas/tests/test_index.py
index 3c9dbd2e48cb6..9f84f5db2a3c9 100644
--- a/pandas/tests/test_index.py
+++ b/pandas/tests/test_index.py
@@ -1909,6 +1909,46 @@ def test_astype(self):
         self.assertTrue(i.equals(result))
         self.check_is_index(result)
 
+    def test_promote_type(self):
+        # GH-9966
+        index_int = Int64Index(np.arange(5))
+        operators = (operator.add,
+                     operator.sub,
+                     operator.mul,
+                     operator.truediv,
+                     operator.floordiv)
+        for op in operators:
+            index_promoted = op(index_int, np.pi)
+            self.assertEqual(index_promoted.dtype, np.float64)
+            self.assertIsInstance(index_promoted, Float64Index)
+
+    def test_promote_type_inplace(self):
+        # Related to GH-9966
+        index = Int64Index(np.arange(5))
+        index += np.pi
+        self.assertEqual(index.dtype, np.float64)
+        self.assertIsInstance(index, Float64Index)
+
+        index = Int64Index(np.arange(5))
+        index -= np.pi
+        self.assertEqual(index.dtype, np.float64)
+        self.assertIsInstance(index, Float64Index)
+
+        index = Int64Index(np.arange(5))
+        index *= np.pi
+        self.assertEqual(index.dtype, np.float64)
+        self.assertIsInstance(index, Float64Index)
+
+        index = Int64Index(np.arange(5))
+        index /= np.pi
+        self.assertEqual(index.dtype, np.float64)
+        self.assertIsInstance(index, Float64Index)
+
+        index = Int64Index(np.arange(5))
+        index //= np.pi
+        self.assertEqual(index.dtype, np.float64)
+        self.assertIsInstance(index, Float64Index)
+
     def test_equals(self):
 
         i = Float64Index([1.0,2.0])