diff --git a/flow360/component/simulation/user_code/core/types.py b/flow360/component/simulation/user_code/core/types.py
index 4ceb96017..3eacd96bb 100644
--- a/flow360/component/simulation/user_code/core/types.py
+++ b/flow360/component/simulation/user_code/core/types.py
@@ -828,7 +828,9 @@ def _serializer(value, info) -> dict:
                         pass
 
                 if isinstance(evaluated, Number):
-                    serialized.evaluated_value = evaluated
+                    serialized.evaluated_value = (
+                        evaluated if not np.isnan(evaluated) else None  # NaN-None handling
+                    )
                 elif isinstance(evaluated, unyt_array):
                     if evaluated.size == 1:
                         serialized.evaluated_value = (
@@ -845,6 +847,8 @@ def _serializer(value, info) -> dict:
                     serialized.evaluated_units = str(evaluated.units.expr)
             else:
                 serialized = SerializedValueOrExpression(type_name="number")
+                # Note: NaN handling should be unnecessary since it would
+                # have end up being expression first so not reaching here.
                 if isinstance(value, (Number, List)):
                     serialized.value = value
                 elif isinstance(value, unyt_array):
diff --git a/tests/simulation/test_expressions.py b/tests/simulation/test_expressions.py
index 865c3b3df..1a9fd2d11 100644
--- a/tests/simulation/test_expressions.py
+++ b/tests/simulation/test_expressions.py
@@ -1,6 +1,6 @@
 import json
 import re
-from typing import Annotated
+from typing import Annotated, Optional
 
 import numpy as np
 import pydantic as pd
@@ -433,17 +433,21 @@ def test_serializer(
 ):
     class TestModel(Flow360BaseModel):
         field: ValueOrExpression[VelocityType] = pd.Field()
+        non_dim_field: Optional[ValueOrExpression[float]] = pd.Field(default=None)
 
     x = UserVariable(name="x", value=4)
+    cp = UserVariable(name="my_cp", value=solution.Cp)
 
-    model = TestModel(field=x * u.m / u.s + 4 * x**2 * u.m / u.s)
+    model = TestModel(field=x * u.m / u.s + 4 * x**2 * u.m / u.s, non_dim_field=cp)
 
     assert str(model.field) == "x * u.m / u.s + 4 * x ** 2 * u.m / u.s"
 
-    serialized = model.model_dump(exclude_none=True)
+    serialized = model.model_dump()
 
     assert serialized["field"]["type_name"] == "expression"
     assert serialized["field"]["expression"] == "x * u.m / u.s + 4 * x ** 2 * u.m / u.s"
+    assert serialized["non_dim_field"]["expression"] == "my_cp"
+    assert serialized["non_dim_field"]["evaluated_value"] == None  # Not NaN anymore
 
     model = TestModel(field=4 * u.m / u.s)