diff --git a/CHANGELOG.md b/CHANGELOG.md
index 01146fc..06ad824 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+## v2.3.1 (2025-12-23)
+
+### Fix
+
+- **core**: handle duplicate IO ids and output mapping
+
 ## v2.3.0 (2025-12-23)
 
 ### Feat
diff --git a/pyproject.toml b/pyproject.toml
index a56d0cc..cb118cf 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,7 +1,7 @@
 [project]
 name = "funcnodes-core"
 
-version = "2.3.0"
+version = "2.3.1"
 
 description = "core package for funcnodes"
 authors = [{name = "Julian Kimmig", email = "julian.kimmig@linkdlab.de"}]
diff --git a/src/funcnodes_core/node.py b/src/funcnodes_core/node.py
index 315d8de..505305a 100644
--- a/src/funcnodes_core/node.py
+++ b/src/funcnodes_core/node.py
@@ -377,7 +377,7 @@ def __init_subclass__(cls, **kwargs):
                     cls,
                     io.uuid,
                 )
-                ipser = ip.to_dict()
+                ipser = io.serialize()
 
             cls._class_io_serialized[ipser["id"]] = ipser
 
diff --git a/src/funcnodes_core/nodemaker.py b/src/funcnodes_core/nodemaker.py
index 859d95a..7cb4673 100644
--- a/src/funcnodes_core/nodemaker.py
+++ b/src/funcnodes_core/nodemaker.py
@@ -107,9 +107,9 @@ async def _wrapped_func(self: Node, *args, **kwargs):
         outs = await asyncfunc(*args, **kwargs)
         if len(outputs) > 1:
             for op, out in zip(outputs, outs):
-                self.outputs[op.name].value = out
+                self.outputs[op.uuid].value = out
         elif len(outputs) == 1:
-            self.outputs[outputs[0].name].value = outs
+            self.outputs[outputs[0].uuid].value = outs
         return outs
 
     kwargs.setdefault("node_name", in_func.ef_funcmeta.get("name", id))
diff --git a/tests/test_decorator.py b/tests/test_decorator.py
index 9de58de..75ebecb 100644
--- a/tests/test_decorator.py
+++ b/tests/test_decorator.py
@@ -4,6 +4,7 @@
 
 
 import funcnodes_core as fn
+import pytest
 from pytest_funcnodes import funcnodes_test
 
 
@@ -600,3 +601,63 @@ def my_node(
     await fn.run_until_complete(ins1, ins2)
     assert ins1.outputs["c"].value == 1
     assert ins2.outputs["c"].value == 3
+
+
+@funcnodes_test
+async def test_decorator_withdouble_params():
+    @fn.NodeDecorator(node_id="my_nodea", outputs=[{"name": "a"}])
+    def my_nodea(a: int, b: int) -> int:
+        return a + b
+
+    node = my_nodea()
+    input_a = node.inputs["a"]
+    output_a = next(op for op in node.outputs.values() if op.name == "a")
+
+    assert input_a.name == "a"
+    assert output_a.name == "a"
+    assert output_a.uuid != input_a.uuid
+    assert output_a.uuid == "a_"
+    assert output_a.uuid in my_nodea._class_io_serialized
+
+    node.inputs["a"].value = 1
+    node.inputs["b"].value = 2
+    await node
+
+    assert node.outputs[output_a.uuid].value == 3
+
+    class MultiOutputNode(fn.Node):
+        node_id = "my_nodea_multi"
+
+        a = fn.NodeInput(id="a", type=int)
+        b = fn.NodeInput(id="b", type=int)
+        out_a1 = fn.NodeOutput(id="a", type=int)
+        out_a2 = fn.NodeOutput(id="a", type=int)
+        out_a3 = fn.NodeOutput(id="a", type=int)
+
+        async def func(self, a: int, b: int) -> int:  # noqa: A003 - signature
+            return a + b
+
+    node_multi = MultiOutputNode()
+    output_uuids = sorted(
+        op.uuid for op in node_multi.outputs.values() if op.name == "a"
+    )
+    assert output_uuids == ["a_", "a__", "a___"]
+    for uuid in output_uuids:
+        assert uuid in MultiOutputNode._class_io_serialized
+
+    with pytest.raises(
+        ValueError, match="automatically generating a new one seems to fail"
+    ):
+
+        class MultiOutputNodeFail(fn.Node):
+            node_id = "my_nodea_multi_fail"
+
+            a = fn.NodeInput(id="a", type=int)
+            b = fn.NodeInput(id="b", type=int)
+            out_a1 = fn.NodeOutput(id="a", type=int)
+            out_a2 = fn.NodeOutput(id="a", type=int)
+            out_a3 = fn.NodeOutput(id="a", type=int)
+            out_a4 = fn.NodeOutput(id="a", type=int)
+
+            async def func(self, a: int, b: int) -> int:  # noqa: A003 - signature
+                return a + b
diff --git a/uv.lock b/uv.lock
index 2f13528..7997790 100644
--- a/uv.lock
+++ b/uv.lock
@@ -457,7 +457,7 @@ wheels = [
 
 [[package]]
 name = "funcnodes-core"
-version = "2.3.0"
+version = "2.3.1"
 source = { editable = "." }
 dependencies = [
     { name = "dill" },