diff --git a/ollama/_utils.py b/ollama/_utils.py
index 15f1cc0c..b1cffbc3 100644
--- a/ollama/_utils.py
+++ b/ollama/_utils.py
@@ -54,15 +54,17 @@ def _parse_docstring(doc_string: Union[str, None]) -> dict[str, str]:
 
 
 def convert_function_to_tool(func: Callable) -> Tool:
+  signature = inspect.signature(func)
   doc_string_hash = str(hash(inspect.getdoc(func)))
   parsed_docstring = _parse_docstring(inspect.getdoc(func))
   schema = type(
     func.__name__,
     (pydantic.BaseModel,),
     {
-      '__annotations__': {k: v.annotation if v.annotation != inspect._empty else str for k, v in inspect.signature(func).parameters.items()},
-      '__signature__': inspect.signature(func),
+      '__annotations__': {k: v.annotation if v.annotation != inspect._empty else str for k, v in signature.parameters.items()},
+      '__signature__': signature,
       '__doc__': parsed_docstring[doc_string_hash],
+      **{k: v.default for k, v in signature.parameters.items() if v.default is not inspect.Parameter.empty},
     },
   ).model_json_schema()
 
@@ -70,7 +72,8 @@ def convert_function_to_tool(func: Callable) -> Tool:
     # If type is missing, the default is string
     types = {t.get('type', 'string') for t in v.get('anyOf')} if 'anyOf' in v else {v.get('type', 'string')}
     if 'null' in types:
-      schema['required'].remove(k)
+      if k in schema.get('required', []):
+        schema['required'].remove(k)
       types.discard('null')
 
     schema['properties'][k] = {
diff --git a/tests/test_utils.py b/tests/test_utils.py
index cb9e0d4f..1a24c214 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -1,10 +1,52 @@
 import json
 import sys
+from enum import IntEnum
 from typing import Dict, List, Mapping, Sequence, Set, Tuple, Union
 
 from ollama._utils import convert_function_to_tool
 
 
+def test_function_defaults_are_not_required():
+  def search(query: str, limit: int = 5):
+    return query, limit
+
+  parameters = convert_function_to_tool(search).function.parameters
+  assert parameters.required == ['query']
+  assert parameters.properties['limit'].type == 'integer'
+
+
+def test_function_default_with_custom_comparison():
+  class DefaultLimit(IntEnum):
+    FIVE = 5
+
+    def __ne__(self, other):
+      raise RuntimeError('Default value comparison is not supported')
+
+  def search(query: str, limit: int = DefaultLimit.FIVE):
+    return query, limit
+
+  parameters = convert_function_to_tool(search).function.parameters
+  assert parameters.required == ['query']
+  assert parameters.properties['limit'].type == 'integer'
+
+
+def test_nullable_default_with_no_required_arguments():
+  def search(query: Union[str, None] = None):
+    return query
+
+  parameters = convert_function_to_tool(search).function.parameters
+  assert not parameters.required
+  assert parameters.properties['query'].type == 'string'
+
+
+def test_keyword_only_defaults_are_not_required():
+  def search(query: str, *, limit: int = 5):
+    return query, limit
+
+  parameters = convert_function_to_tool(search).function.parameters
+  assert parameters.required == ['query']
+
+
 def test_function_to_tool_conversion():
   def add_numbers(x: int, y: Union[int, None] = None) -> int:
     """Add two numbers together.