diff --git a/cubed/core/ops.py b/cubed/core/ops.py
index 37202559..d9154183 100644
--- a/cubed/core/ops.py
+++ b/cubed/core/ops.py
@@ -816,9 +816,9 @@ def key_function(out_key):
         key_function,
         x,
         shapes=[shape],
-        dtypes=[x.dtype],
+        dtypes=[dtype],
         chunkss=[chunks],
-        extra_func_kwargs=dict(func=func, dtype=dtype),
+        extra_func_kwargs=dict(func=func, dtype=x.dtype),
         num_input_blocks=num_input_blocks,
         iterable_input_blocks=iterable_input_blocks,
         selection_function=selection_function,
diff --git a/cubed/tests/test_overlap.py b/cubed/tests/test_overlap.py
index 5c29e3a7..a388a3ca 100644
--- a/cubed/tests/test_overlap.py
+++ b/cubed/tests/test_overlap.py
@@ -39,6 +39,24 @@ def test_map_overlap_1d_single_chunk():
     assert_array_equal(b.compute(), np.array([0, 0, 1, 2, 3, 4, 5, 0]))
 
 
+def test_map_overlap_1d_change_dtype():
+    x = np.arange(6)
+    a = xp.asarray(x, chunks=(3,))
+
+    b = cubed.map_overlap(
+        lambda x: x.astype(np.float64),
+        a,
+        dtype=np.float64,
+        chunks=((5, 5),),
+        depth=1,
+        boundary=0,
+        trim=False,
+    )
+
+    assert b.dtype == np.float64
+    assert_array_equal(b.compute(), np.array([0, 0, 1, 2, 3, 2, 3, 4, 5, 0]))
+
+
 def test_map_overlap_2d():
     x = np.arange(36).reshape((6, 6))
     a = xp.asarray(x, chunks=(3, 3))