diff --git a/test/unit/test_disk_tensor.py b/test/unit/test_disk_tensor.py
index 3e8f0ae17a..6d215b627a 100644
--- a/test/unit/test_disk_tensor.py
+++ b/test/unit/test_disk_tensor.py
@@ -355,9 +355,9 @@ class TestDiskTensor(unittest.TestCase):
     t[0:8].assign(Tensor([12345], dtype=dtypes.int64, device="CPU").bitcast(dtypes.uint8))
     val = int.from_bytes(t[0:8].data(), 'little')
     self.assertEqual(val, 12345)
-    # bitcast on target with mismatched dtype raises
+    # bitcast on target with non-broadcastable dtype raises
     with self.assertRaises(RuntimeError):
-      t[0:8].bitcast(dtypes.int64).assign(Tensor([12345], dtype=dtypes.int32))
+      t[0:4].bitcast(dtypes.int32).assign(Tensor([12345], dtype=dtypes.int64))
 
   def test_assign_cross_device(self):
     # disk assign allows cross-device (source on GPU/CPU, target on disk)
diff --git a/tinygrad/tensor.py b/tinygrad/tensor.py
index c2edc7763f..f7a09b4116 100644
--- a/tinygrad/tensor.py
+++ b/tinygrad/tensor.py
@@ -286,21 +286,20 @@ class Tensor(OpMixin):
     return self
 
   def assign(self, x:Tensor|PyConst|list|tuple) -> Tensor:
-    # TODO: this is a hack for writing to DISK. remove with working assign
-    if isinstance(self.device, str) and self.device.startswith("DISK"):
-      if not isinstance(x, Tensor): x = Tensor(x, device="CPU", dtype=self.dtype)
-      if self.dtype != x.dtype: raise RuntimeError(f"DISK assign dtype mismatch {self.dtype} != {x.dtype}")
-      self._buffer().copyin(x._data())
-      return self
-    if not isinstance(x, Tensor): x = Tensor(x, device=self.device, dtype=self.dtype)
+    is_disk = isinstance(self.device, str) and self.device.startswith("DISK")
+    if not isinstance(x, Tensor): x = Tensor(x, device="CPU" if is_disk else self.device, dtype=self.dtype)
     if self.uop is x.uop: return self  # a self assign is a NOOP
-    # NOTE: we allow cross device assign
     # broadcast x
     if least_upper_dtype(self.dtype, x.dtype) == self.dtype: x = x._broadcast_to(self.shape).cast(self.dtype)
-    assert self.shape == x.shape, f"assign shape mismatch {self.shape} != {x.shape}"
-    assert self.device == x.device, f"assign device mismatch {self.device} != {x.device}"
-    assert self.dtype == x.dtype, f"assign dtype mismatch {self.dtype} != {x.dtype}"
-    assert not isinstance(self.device, tuple) or self.uop.axis == x.uop.axis, f"multi assign axis mismatch {self.uop.axis} != {x.uop.axis}"
+    if self.shape != x.shape: raise RuntimeError(f"assign shape mismatch {self.shape} != {x.shape}")
+    if not is_disk and self.device != x.device: raise RuntimeError(f"assign device mismatch {self.device} != {x.device}")
+    if self.dtype != x.dtype: raise RuntimeError(f"assign dtype mismatch {self.dtype} != {x.dtype}")
+    if isinstance(self.device, tuple) and self.uop.axis != x.uop.axis: raise RuntimeError(f"multi axis mismatch {self.uop.axis} != {x.uop.axis}")
+
+    # TODO: this is a hack for writing to DISK. remove with working assign
+    if is_disk:
+      self._buffer().copyin(x._data())
+      return self
     return self.replace(self._apply_uop(UOp.assign, x))
 
   def detach(self) -> Tensor: