diff --git a/python/dask_cudf/dask_cudf/sorting.py b/python/dask_cudf/dask_cudf/sorting.py
index f9058ed9aed..5e17a3aa29f 100644
--- a/python/dask_cudf/dask_cudf/sorting.py
+++ b/python/dask_cudf/dask_cudf/sorting.py
@@ -29,9 +29,10 @@ def _set_partitions_pre(s, divisions, ascending=True):
         partitions = (
             len(divisions) - divisions.searchsorted(s, side="right") - 1
         )
-    partitions[
-        divisions.tail(1).searchsorted(s, side="right").astype("bool")
-    ] = ((len(divisions) - 2) if ascending else 0)
+    partitions[(partitions < 0) | (partitions >= len(divisions) - 1)] = (
+        0 if ascending else (len(divisions) - 2)
+    )
+    partitions[s._columns[0].isna().values] = len(divisions) - 2
     return partitions
 
 
@@ -206,7 +207,7 @@ def quantile_divisions(df, by, npartitions):
                 divisions[col].iloc[-1] = chr(
                     ord(divisions[col].iloc[-1][0]) + 1
                 )
-        divisions = divisions.drop_duplicates()
+        divisions = divisions.drop_duplicates().sort_index()
     return divisions
 
 
diff --git a/python/dask_cudf/dask_cudf/tests/test_sort.py b/python/dask_cudf/dask_cudf/tests/test_sort.py
index a93a3c783fa..036b2a9f50c 100644
--- a/python/dask_cudf/dask_cudf/tests/test_sort.py
+++ b/python/dask_cudf/dask_cudf/tests/test_sort.py
@@ -1,3 +1,4 @@
+import cupy as cp
 import numpy as np
 import pytest
 
@@ -7,7 +8,6 @@
 import cudf
 
 import dask_cudf
-from dask_cudf.sorting import quantile_divisions
 
 
 @pytest.mark.parametrize("ascending", [True, False])
@@ -26,7 +26,9 @@ def test_sort_values(nelem, nparts, by, ascending):
     with dask.config.set(scheduler="single-threaded"):
         got = ddf.sort_values(by=by, ascending=ascending)
     expect = df.sort_values(by=by, ascending=ascending)
-    dd.assert_eq(got, expect, check_index=False)
+
+    # check that sorted indices are identical
+    dd.assert_eq(got.reset_index(), expect.reset_index(), check_index=False)
 
 
 @pytest.mark.parametrize("ascending", [True, False])
@@ -56,23 +58,25 @@ def test_sort_repartition():
 
 @pytest.mark.parametrize("ascending", [True, False])
 @pytest.mark.parametrize("by", ["a", "b", ["a", "b"]])
-def test_sort_values_with_nulls(by, ascending):
-    df = cudf.DataFrame(
+@pytest.mark.parametrize(
+    "data",
+    [
         {
             "a": list(range(50)) + [None] * 50 + list(range(50, 100)),
             "b": [None] * 100 + list(range(100, 150)),
-        }
-    )
-    ddf = dd.from_pandas(df, npartitions=10)
-
-    # assert that quantile divisions of dataframe contains nulls
-    divisions = quantile_divisions(ddf, by, ddf.npartitions)
-    if isinstance(divisions, list):
-        assert None in divisions
-    else:
-        assert all([divisions[col].has_nulls for col in by])
+        },
+        {"a": list(range(15)) + [None] * 5, "b": list(reversed(range(20)))},
+    ],
+)
+def test_sort_values_with_nulls(data, by, ascending):
+    np.random.seed(0)
+    cp.random.seed(0)
+    df = cudf.DataFrame(data)
+    ddf = dd.from_pandas(df, npartitions=5)
 
     with dask.config.set(scheduler="single-threaded"):
         got = ddf.sort_values(by=by, ascending=ascending)
-    expect = df.sort_values(by=by, ascending=ascending)
-    dd.assert_eq(got, expect)
+        expect = df.sort_values(by=by, ascending=ascending)
+
+    # check that sorted indices are identical
+    dd.assert_eq(got.reset_index(), expect.reset_index(), check_index=False)