diff --git a/comfy_api/latest/_io.py b/comfy_api/latest/_io.py
index 4942ed46c..e50266bc5 100644
--- a/comfy_api/latest/_io.py
+++ b/comfy_api/latest/_io.py
@@ -395,7 +395,6 @@ class Combo(ComfyTypeIO):
 @comfytype(io_type="COMBO")
 class MultiCombo(ComfyTypeI):
     '''Multiselect Combo input (dropdown for selecting potentially more than one value).'''
-    # TODO: something is wrong with the serialization, frontend does not recognize it as multiselect
     Type = list[str]
     class Input(Combo.Input):
         def __init__(self, id: str, options: list[str], display_name: str=None, optional=False, tooltip: str=None, lazy: bool=None,
@@ -408,12 +407,14 @@ class MultiCombo(ComfyTypeI):
             self.default: list[str]
 
         def as_dict(self):
-            to_return = super().as_dict() | prune_dict({
-                "multi_select": self.multiselect,
-                "placeholder": self.placeholder,
-                "chip": self.chip,
+            # Frontend expects `multi_select` to be an object config (not a boolean).
+            # Keep top-level `multiselect` from Combo.Input for backwards compatibility.
+            return super().as_dict() | prune_dict({
+                "multi_select": prune_dict({
+                    "placeholder": self.placeholder,
+                    "chip": self.chip,
+                }),
             })
-            return to_return
 
 @comfytype(io_type="IMAGE")
 class Image(ComfyTypeIO):
diff --git a/execution.py b/execution.py
index 654db8426..f37d0360d 100644
--- a/execution.py
+++ b/execution.py
@@ -1019,7 +1019,12 @@ async def validate_inputs(prompt_id, prompt, item, validated, visiting=None):
                         combo_options = extra_info.get("options", [])
                     else:
                         combo_options = input_type
-                    if val not in combo_options:
+                    is_multiselect = extra_info.get("multiselect", False)
+                    if is_multiselect and isinstance(val, list):
+                        invalid_vals = [v for v in val if v not in combo_options]
+                    else:
+                        invalid_vals = [val] if val not in combo_options else []
+                    if invalid_vals:
                         input_config = info
                         list_info = ""
 
@@ -1034,7 +1039,7 @@ async def validate_inputs(prompt_id, prompt, item, validated, visiting=None):
                         error = {
                             "type": "value_not_in_list",
                             "message": "Value not in list",
-                            "details": f"{x}: '{val}' not in {list_info}",
+                            "details": f"{x}: {', '.join(repr(v) for v in invalid_vals)} not in {list_info}",
                             "extra_info": {
                                 "input_name": x,
                                 "input_config": input_config,
diff --git a/nodes.py b/nodes.py
index 1e41b2ae0..cf61d9df0 100644
--- a/nodes.py
+++ b/nodes.py
@@ -2262,7 +2262,7 @@ async def load_custom_node(module_path: str, ignore=set(), module_parent="custom
                 logging.warning(f"Error while calling comfy_entrypoint in {module_path}: {e}")
                 return False
         else:
-            logging.warning(f"Skip {module_path} module for custom nodes due to the lack of NODE_CLASS_MAPPINGS or NODES_LIST (need one).")
+            logging.warning(f"Skip {module_path} module for custom nodes due to the lack of NODE_CLASS_MAPPINGS or comfy_entrypoint (need one).")
             return False
     except Exception as e:
         logging.warning(traceback.format_exc())
diff --git a/tests-unit/comfy_api_test/multicombo_serialization_test.py b/tests-unit/comfy_api_test/multicombo_serialization_test.py
new file mode 100644
index 000000000..421c65a0d
--- /dev/null
+++ b/tests-unit/comfy_api_test/multicombo_serialization_test.py
@@ -0,0 +1,78 @@
+from comfy_api.latest._io import Combo, MultiCombo
+
+
+def test_multicombo_serializes_multi_select_as_object():
+    multi_combo = MultiCombo.Input(
+        id="providers",
+        options=["a", "b", "c"],
+        default=["a"],
+    )
+
+    serialized = multi_combo.as_dict()
+
+    assert serialized["multiselect"] is True
+    assert "multi_select" in serialized
+    assert serialized["multi_select"] == {}
+
+
+def test_multicombo_serializes_multi_select_with_placeholder_and_chip():
+    multi_combo = MultiCombo.Input(
+        id="providers",
+        options=["a", "b", "c"],
+        default=["a"],
+        placeholder="Select providers",
+        chip=True,
+    )
+
+    serialized = multi_combo.as_dict()
+
+    assert serialized["multiselect"] is True
+    assert serialized["multi_select"] == {
+        "placeholder": "Select providers",
+        "chip": True,
+    }
+
+
+def test_combo_does_not_serialize_multiselect():
+    """Regular Combo should not have multiselect in its serialized output."""
+    combo = Combo.Input(
+        id="choice",
+        options=["a", "b", "c"],
+    )
+
+    serialized = combo.as_dict()
+
+    # Combo sets multiselect=False, but prune_dict keeps False (not None),
+    # so it should be present but False
+    assert serialized.get("multiselect") is False
+    assert "multi_select" not in serialized
+
+
+def _validate_combo_values(val, combo_options, is_multiselect):
+    """Reproduce the validation logic from execution.py for testing."""
+    if is_multiselect and isinstance(val, list):
+        return [v for v in val if v not in combo_options]
+    else:
+        return [val] if val not in combo_options else []
+
+
+def test_multicombo_validation_accepts_valid_list():
+    options = ["a", "b", "c"]
+    assert _validate_combo_values(["a", "b"], options, True) == []
+
+
+def test_multicombo_validation_rejects_invalid_values():
+    options = ["a", "b", "c"]
+    assert _validate_combo_values(["a", "x"], options, True) == ["x"]
+
+
+def test_multicombo_validation_accepts_empty_list():
+    options = ["a", "b", "c"]
+    assert _validate_combo_values([], options, True) == []
+
+
+def test_combo_validation_rejects_list_even_with_valid_items():
+    """A regular Combo should not accept a list value."""
+    options = ["a", "b", "c"]
+    invalid = _validate_combo_values(["a", "b"], options, False)
+    assert len(invalid) > 0