diff --git a/test/null/test_gpudims.py b/test/null/test_gpudims.py
index 8324e29a8c..b18ff6c1ac 100644
--- a/test/null/test_gpudims.py
+++ b/test/null/test_gpudims.py
@@ -66,6 +66,8 @@ class TestGroupedDims(unittest.TestCase):
     self._check_grouped_dims("gidx", (65536,2), (65535,65535,65535), False, [32768,4], False)
     # test when the only divisor is the square root of dim
     self._check_grouped_dims("gidx", (121,), (12,12,12), False, [11,11], False)
+    #                              2             ->             3
+    self._check_grouped_dims("gidx", (128,128), (16,16,256), False, [16,16,64], False)
 
     # collapse on onto the left most axis
     self._check_grouped_dims("gidx", (2,3,4,5), (16,16,16), False, [6,4,5])
@@ -85,8 +87,11 @@ class TestGroupedDims(unittest.TestCase):
     with self.assertRaises(RuntimeError):
       get_grouped_dims("gidx", (2,3,4,5,6), (16,16,16))
 
-  def test_split_2d_to_3d(self):
-    self._check_grouped_dims("gidx", (128,128), (16,16,256), False, [16,16,64], False)
+  def test_grouped_direct_dims_are_special(self):
+    # when (2,3) are merged into 6, the unmerged dims (4,5) should map directly to SPECIAL ops (no div/mod)
+    idxs = get_grouped_dims("gidx", (2,3,4,5), (16,16,16), False)
+    assert idxs[2].op is Ops.SPECIAL, f"expected SPECIAL for direct-mapped dim, got {idxs[2].op}"
+    assert idxs[3].op is Ops.SPECIAL, f"expected SPECIAL for direct-mapped dim, got {idxs[3].op}"
 
   def test_max_sizes_none(self):
     self._check_grouped_dims("gidx", (2,3,4), None, False, [2,3,4])