From 8a2c23d3dc7f392b022b89ca5ce94f345b53fa56 Mon Sep 17 00:00:00 2001
From: chenyu <chenyu@fastmail.com>
Date: Mon, 9 Feb 2026 10:37:08 -0500
Subject: [PATCH] raise RuntimeError for setitem dtype mismatch (#14642)

---
 test/test_setitem.py | 18 +++++++++++-------
 tinygrad/tensor.py   |  3 ++-
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/test/test_setitem.py b/test/test_setitem.py
index 82f37f5324..1f6cdc02d6 100644
--- a/test/test_setitem.py
+++ b/test/test_setitem.py
@@ -13,7 +13,7 @@ class TestSetitem(unittest.TestCase):
       ((6,6), (slice(2,4), slice(3,5)), 1.0),
       ((6,6), (3, 4), 1.0),
       ((6,6), (3, None, 4, None), 1.0),
-      ((4,4,4,4), (Ellipsis, slice(1,3), slice(None)), Tensor(4)),
+      ((4,4,4,4), (Ellipsis, slice(1,3), slice(None)), Tensor(4.0)),
       ((4,4,4,4), (Ellipsis, slice(1,3)), 4),
       ((4,4,4,4), (2, slice(1,3), None, 1), 4),
       ((4,4,4,4), (slice(1,3), slice(None), slice(0,4,2)), 4),
@@ -50,6 +50,10 @@ class TestSetitem(unittest.TestCase):
         t[1] = v
         self.assertEqual(t.dtype, dt)
 
+  def test_setitem_dtype_mismatch(self):
+    t = Tensor.zeros(6, dtype=dtypes.float).contiguous().realize()
+    with self.assertRaises(RuntimeError): t[2:4] = Tensor([1, 2], dtype=dtypes.int)
+
   def test_setitem_into_noncontiguous(self):
     t = Tensor.ones(4)
     with self.assertRaises(RuntimeError): t[1] = 5
@@ -193,23 +197,23 @@ class TestSetitem(unittest.TestCase):
 
   def test_setitem_advanced_indexing(self):
     # Example from https://numpy.org/doc/stable/user/basics.indexing.html#combining-advanced-and-basic-indexing
-    t = Tensor.zeros(10,20,30,40,50).contiguous()
+    t = Tensor.zeros(10,20,30,40,50, dtype=dtypes.int).contiguous()
     ind_1 = Tensor([5,3,7,8])
     ind_2 = Tensor([[[0],[1],[2]],[[3],[4],[5]]])
     v = Tensor.arange(2*3*4*10*30*50).reshape(2,3,4,10,30,50)
     t[:, ind_1, :, ind_2, :] = v
-    n = np.zeros((10,20,30,40,50))
+    n = np.zeros((10,20,30,40,50), dtype=np.int32)
     n[:, ind_1.numpy(), :, ind_2.numpy(), :] = v.numpy()
-    np.testing.assert_allclose(t.numpy(), n)
+    np.testing.assert_equal(t.numpy(), n)
 
   def test_setitem_2d_tensor_indexing(self):
-    t = Tensor.zeros(2).contiguous()
+    t = Tensor.zeros(2, dtype=dtypes.int).contiguous()
     index = Tensor([[0, 1], [1,0]])
     v = Tensor.arange(2*2).reshape(2, 2).contiguous()
     t[index] = v
-    n = np.zeros((2,))
+    n = np.zeros((2,), dtype=np.int32)
     n[index.numpy()] = v.numpy()
-    np.testing.assert_allclose(t.numpy(), n)
+    np.testing.assert_equal(t.numpy(), n)
 
   @unittest.skip("slow")
   def test_setitem_tensor_indexing_fuzz(self):
diff --git a/tinygrad/tensor.py b/tinygrad/tensor.py
index 6eedeccd9a..86c072a60e 100644
--- a/tinygrad/tensor.py
+++ b/tinygrad/tensor.py
@@ -1279,6 +1279,7 @@ class Tensor(OpMixin):
     return self._getitem(indices)
 
   def __setitem__(self, indices, v:Tensor|PyConst|list|tuple) -> None:
+    if isinstance(v, Tensor) and v.dtype != self.dtype: raise RuntimeError(f"setitem dtype mismatch: {self.dtype=} != {v.dtype=}")
     if isinstance(self.device, str) and self.device.startswith("DISK"):
       self.realize()._getitem(indices).assign(v)
       return
@@ -1291,7 +1292,7 @@ class Tensor(OpMixin):
     else: # basic setitem
       self.realize()
       if not self.uop.is_writable_view(): raise RuntimeError("setitem target must be a writable view backed by a buffer")
-      res.assign(v.cast(res.dtype)).realize()
+      res.assign(v).realize()
 
   def __delitem__(self, indices) -> None:
     raise TypeError("Tensor does not support deleting items")