diff --git a/mlx_lm/models/qwen3_5_full.py b/mlx_lm/models/qwen3_5_full.py
--- a/mlx_lm/models/qwen3_5_full.py
+++ b/mlx_lm/models/qwen3_5_full.py
@@ -459,9 +459,9 @@ class Model(nn.Module):
                 settings.get("group_size"),
                 settings.get("mode", "affine"),
             )
-            if (bits, group, mode) != (4, 64, "affine"):
+            if bits not in (4, 5) or group != 64 or mode != "affine":
                 raise ValueError(
-                    "This extension only prepares affine/4-bit/group-64 native checkpoints"
+                    "This extension only prepares affine/4-or-5-bit/group-64 native checkpoints"
                 )
             original = shapes[f"{path}.weight"]
             if original[-1] % group:
diff --git a/tests/test_qwen3_5_full.py b/tests/test_qwen3_5_full.py
--- a/tests/test_qwen3_5_full.py
+++ b/tests/test_qwen3_5_full.py
@@ -340,14 +340,17 @@ def test_official_nonquantized_convert_and_reload_preserve_all_tensors(
         load_model(output, lazy=True)
 
 
-def test_fixed_affine_quantized_roundtrip_preserves_component_tree(reference, tmp_path):
+@pytest.mark.parametrize("bits", [4, 5])
+def test_fixed_affine_quantized_roundtrip_preserves_component_tree(
+    reference, tmp_path, bits
+):
     from mlx_lm.utils import quantize_model, save_model
 
     config, _, _, state, _ = reference
     model = Model(ModelArgs.from_dict(config))
     model.load_weights(list(model.sanitize(state).items()), strict=True)
     original_names = set(dict(tree_flatten(model.parameters())))
-    model, quantized_config = quantize_model(model, config, 64, 4, mode="affine")
+    model, quantized_config = quantize_model(model, config, 64, bits, mode="affine")
     save_model(tmp_path, model)
     save_config(quantized_config, tmp_path / "config.json")
     loaded, saved_config = load_model(tmp_path, lazy=False, strict=True)
@@ -355,7 +358,7 @@ def test_fixed_affine_quantized_roundtrip_preserves_component_tree(reference, tm
     assert set(actual) == set(expected)
     assert original_names <= set(actual)
     assert saved_config["quantization"] == {
-        "bits": 4,
+        "bits": bits,
         "group_size": 64,
         "mode": "affine",
     }