diff --git a/python/cudf/cudf/core/groupby/groupby.py b/python/cudf/cudf/core/groupby/groupby.py
index b5538a0f0a8..8347c2bd94e 100644
--- a/python/cudf/cudf/core/groupby/groupby.py
+++ b/python/cudf/cudf/core/groupby/groupby.py
@@ -201,11 +201,11 @@ def cumcount(self):
             cudf.Series(
                 cudf.core.column.column_empty(
                     len(self.obj), "int8", masked=False
-                )
+                ),
+                index=self.obj.index,
             )
             .groupby(self.grouping, sort=self._sort)
             .agg("cumcount")
-            .reset_index(drop=True)
         )
 
     def rank(
@@ -343,7 +343,6 @@ def agg(self, func):
 
         if not self._as_index:
             result = result.reset_index()
-
         if libgroupby._is_all_scan_aggregate(normalized_aggs):
             # Scan aggregations return rows in original index order
             return self._mimic_pandas_order(result)
diff --git a/python/cudf/cudf/tests/test_groupby.py b/python/cudf/cudf/tests/test_groupby.py
index 99ee95a8f18..0750a36461b 100644
--- a/python/cudf/cudf/tests/test_groupby.py
+++ b/python/cudf/cudf/tests/test_groupby.py
@@ -1116,13 +1116,15 @@ def test_groupby_size():
     )
 
 
-def test_groupby_cumcount():
+@pytest.mark.parametrize("index", [None, [1, 2, 3, 4]])
+def test_groupby_cumcount(index):
     pdf = pd.DataFrame(
         {
             "a": [1, 1, 3, 4],
             "b": ["bob", "bob", "alice", "cooper"],
             "c": [1, 2, 3, 4],
-        }
+        },
+        index=index,
     )
     gdf = cudf.from_pandas(pdf)
 
@@ -1138,7 +1140,7 @@ def test_groupby_cumcount():
         check_dtype=False,
     )
 
-    sr = pd.Series(range(len(pdf)))
+    sr = pd.Series(range(len(pdf)), index=index)
     assert_groupby_results_equal(
         pdf.groupby(sr).cumcount(),
         gdf.groupby(sr).cumcount(),