diff --git a/src/agents/function_schema.py b/src/agents/function_schema.py
index 8fe52df320..c0d8652b7c 100644
--- a/src/agents/function_schema.py
+++ b/src/agents/function_schema.py
@@ -404,6 +404,21 @@ def function_schema(
                 )
 
     # 3. Dynamically build a Pydantic model
+    # Pydantic raises ValueError for field names that match built-in BaseModel methods in a
+    # protected namespace (e.g. model_dump, model_validate).  Catch these early.
+    _PYDANTIC_PROTECTED_NAMES = {
+        "model_dump",
+        "model_dump_json",
+        "model_validate",
+        "model_validate_json",
+        "model_validate_strings",
+    }
+    colliding = _PYDANTIC_PROTECTED_NAMES.intersection(fields)
+    if colliding:
+        raise UserError(
+            f"Function '{func_name}' has parameter(s) {sorted(colliding)} whose name(s) conflict "
+            "with Pydantic BaseModel built-in methods. Rename the parameter(s) to avoid this."
+        )
     dynamic_model = create_model(f"{func_name}_args", __base__=BaseModel, **fields)
 
     # 4. Build JSON schema from that model
diff --git a/tests/test_function_schema.py b/tests/test_function_schema.py
index 9771bda99d..8aec1692e9 100644
--- a/tests/test_function_schema.py
+++ b/tests/test_function_schema.py
@@ -885,3 +885,13 @@ def func_with_annotated_multiple_field_constraints(
 
     with pytest.raises(ValidationError):  # zero factor
         fs.params_pydantic_model(**{"score": 50, "factor": 0.0})
+
+
+def test_pydantic_protected_namespace_param_raises_user_error():
+    # Parameters named after Pydantic's protected BaseModel methods must raise UserError,
+    # not an opaque ValueError from inside Pydantic's create_model().
+    def func_with_model_validate(model_validate: str, query: str) -> str:
+        return query
+
+    with pytest.raises(UserError, match="model_validate"):
+        function_schema(func_with_model_validate, use_docstring_info=False)