diff --git a/src/hera/workflows/io/v1.py b/src/hera/workflows/io/v1.py
index 9699dbed8..cd75d182f 100644
--- a/src/hera/workflows/io/v1.py
+++ b/src/hera/workflows/io/v1.py
@@ -3,7 +3,7 @@
 from typing import Any, List, Optional, Union
 
 from hera.shared._pydantic import BaseModel, get_fields
-from hera.shared.serialization import serialize
+from hera.shared.serialization import MISSING, serialize
 from hera.workflows.artifact import Artifact
 from hera.workflows.parameter import Parameter
 
@@ -33,27 +33,21 @@ def _get_parameters(cls, object_override: "Optional[RunnerInput]" = None) -> Lis
         annotations = {k: v for k, v in ChainMap(*(get_annotations(c) for c in cls.__mro__)).items()}
 
         fields = get_fields(cls)
-        for field in fields:
+        for field, field_info in fields.items():
             if get_origin(annotations[field]) is Annotated:
                 if isinstance(get_args(annotations[field])[1], Parameter):
                     param = get_args(annotations[field])[1]
                     if object_override:
                         param.default = serialize(getattr(object_override, field))
-                    elif fields[field].default:
+                    elif field_info.default:
                         # Serialize the value (usually done in Parameter's validator)
-                        param.default = serialize(fields[field].default)
+                        param.default = serialize(field_info.default)
                     parameters.append(param)
             else:
                 # Create a Parameter from basic type annotations
-                if object_override:
-                    parameters.append(
-                        Parameter(
-                            name=field,
-                            default=serialize(getattr(object_override, field)),
-                        )
-                    )
-                else:
-                    parameters.append(Parameter(name=field, default=fields[field].default))
+                default = getattr(object_override, field) if object_override else field_info.default
+                parameters.append(Parameter(name=field, default=default or MISSING))
+
         return parameters
 
     @classmethod
diff --git a/src/hera/workflows/io/v2.py b/src/hera/workflows/io/v2.py
index 6512809cc..a8904c2a1 100644
--- a/src/hera/workflows/io/v2.py
+++ b/src/hera/workflows/io/v2.py
@@ -5,7 +5,8 @@
 from collections import ChainMap
 from typing import Any, List, Optional, Union
 
-from hera.shared.serialization import serialize
+
+from hera.shared.serialization import MISSING, serialize
 from hera.workflows.artifact import Artifact
 from hera.workflows.parameter import Parameter
 
@@ -23,6 +24,7 @@
 
 if find_spec("pydantic.v1"):
     from pydantic import BaseModel
+    from pydantic_core import PydanticUndefined
 
     class RunnerInput(BaseModel):
         """Input model usable by the Hera Runner.
@@ -38,22 +40,24 @@ def _get_parameters(cls, object_override: "Optional[RunnerInput]" = None) -> Lis
             parameters = []
             annotations = {k: v for k, v in ChainMap(*(get_annotations(c) for c in cls.__mro__)).items()}
 
-            for field in cls.model_fields:  # type: ignore
+            for field, field_info in cls.model_fields.items():
                 if get_origin(annotations[field]) is Annotated:
                     if isinstance(get_args(annotations[field])[1], Parameter):
                         param = get_args(annotations[field])[1]
                         if object_override:
                             param.default = serialize(getattr(object_override, field))
-                        elif cls.model_fields[field].default:  # type: ignore
+                        elif field_info.default:  # type: ignore
                             # Serialize the value (usually done in Parameter's validator)
-                            param.default = serialize(cls.model_fields[field].default)  # type: ignore
+                            param.default = serialize(field_info.default)  # type: ignore
                         parameters.append(param)
                 else:
                     # Create a Parameter from basic type annotations
-                    if object_override:
-                        parameters.append(Parameter(name=field, default=serialize(getattr(object_override, field))))
-                    else:
-                        parameters.append(Parameter(name=field, default=cls.model_fields[field].default))  # type: ignore
+                    default = getattr(object_override, field) if object_override else field_info.default
+                    if default == PydanticUndefined:
+                        default = MISSING
+
+                    parameters.append(Parameter(name=field, default=default or MISSING))
+
             return parameters
 
         @classmethod
diff --git a/tests/script_annotations/pydantic_io_v1.py b/tests/script_annotations/pydantic_io_v1.py
index ca2663a7f..e04fe9965 100644
--- a/tests/script_annotations/pydantic_io_v1.py
+++ b/tests/script_annotations/pydantic_io_v1.py
@@ -13,6 +13,7 @@
 class ParamOnlyInput(RunnerInput):
     my_int: int = 1
     my_annotated_int: Annotated[int, Parameter(name="another-int", description="my desc")] = 42
+    no_default_param: int
 
 
 class ParamOnlyOutput(RunnerOutput):
@@ -64,14 +65,14 @@ def pydantic_io(
 
 @script(constructor="runner")
 def pydantic_io_with_defaults(
-    my_input: ParamOnlyInput = ParamOnlyInput(my_int=2, my_annotated_int=24),
+    my_input: ParamOnlyInput = ParamOnlyInput(my_int=2, my_annotated_int=24, no_default_param=1),
 ) -> ParamOnlyOutput:
     pass
 
 
 @script(constructor="runner")
 def pydantic_io_within_generic(
-    my_inputs: List[ParamOnlyInput] = [ParamOnlyInput(), ParamOnlyInput(my_int=2)],
+    my_inputs: List[ParamOnlyInput] = [ParamOnlyInput(no_default_param=1), ParamOnlyInput(my_int=2, no_default_param=2)],
 ) -> ParamOnlyOutput:
     pass
 
diff --git a/tests/script_annotations/pydantic_io_v2.py b/tests/script_annotations/pydantic_io_v2.py
index fb2643f74..d83e05ae8 100644
--- a/tests/script_annotations/pydantic_io_v2.py
+++ b/tests/script_annotations/pydantic_io_v2.py
@@ -23,6 +23,7 @@
 class ParamOnlyInput(RunnerInput):
     my_int: int = 1
     my_annotated_int: Annotated[int, Parameter(name="another-int", description="my desc")] = 42
+    no_default_param: int
 
 
 class ParamOnlyOutput(RunnerOutput):
@@ -74,14 +75,14 @@ def pydantic_io(
 
 @script(constructor="runner")
 def pydantic_io_with_defaults(
-    my_input: ParamOnlyInput = ParamOnlyInput(my_int=2, my_annotated_int=24),
+    my_input: ParamOnlyInput = ParamOnlyInput(my_int=2, my_annotated_int=24, no_default_param=1),
 ) -> ParamOnlyOutput:
     pass
 
 
 @script(constructor="runner")
 def pydantic_io_within_generic(
-    my_inputs: List[ParamOnlyInput] = [ParamOnlyInput(), ParamOnlyInput(my_int=2)],
+    my_inputs: List[ParamOnlyInput] = [ParamOnlyInput(no_default_param=1), ParamOnlyInput(my_int=2,no_default_param=2)],
 ) -> ParamOnlyOutput:
     pass
 
diff --git a/tests/test_script_annotations.py b/tests/test_script_annotations.py
index 05ab1ec2d..4f330f1f4 100644
--- a/tests/test_script_annotations.py
+++ b/tests/test_script_annotations.py
@@ -196,6 +196,7 @@ def test_configmap(global_config_fixture):
                 "parameters": [
                     {"name": "my_int", "default": "1"},
                     {"name": "another-int", "default": "42", "description": "my desc"},
+                    {"name": "no_default_param"},
                 ]
             },
             {
@@ -247,6 +248,7 @@ def test_configmap(global_config_fixture):
                 "parameters": [
                     {"name": "my_int", "default": "2"},
                     {"name": "another-int", "default": "24", "description": "my desc"},
+                    {"name": "no_default_param", "default": "1"},
                 ],
             },
             {
@@ -263,7 +265,7 @@ def test_configmap(global_config_fixture):
                 "parameters": [
                     {
                         "name": "my_inputs",
-                        "default": '[{"my_int": 1, "my_annotated_int": 42}, {"my_int": 2, "my_annotated_int": 42}]',
+                        "default": '[{"my_int": 1, "my_annotated_int": 42, "no_default_param": 1}, {"my_int": 2, "my_annotated_int": 42, "no_default_param": 2}]',
                     },
                 ],
             },