diff --git a/ioccontainer/inject.py b/ioccontainer/inject.py
index 162f6e1..98ba622 100644
--- a/ioccontainer/inject.py
+++ b/ioccontainer/inject.py
@@ -50,7 +50,11 @@ def inject_decorator(container: 'Container'):
             service = container.get(cls)
 
             if _is_positional_argument(position, parameter, new_args):
-                new_args.append(service)
+                if len(new_args) >= position + 1:
+                    new_args[position] = service
+                else:
+                    new_args.append(service)
+
             elif _is_keyword_argument(parameter):
                 kwargs[parameter.name] = service
             else:
@@ -96,7 +100,9 @@ def _default_parameter_provided(parameter: inspect.Parameter) -> bool:
 
 def _argument_provided(position: int, parameter: inspect.Parameter,
                        args: typing.List, kwargs: typing.Dict) -> bool:
-    return position < len(args) or parameter.name in kwargs.keys()
+    if position < len(args) and args[position] is not None:
+        return True
+    return kwargs.get(parameter.name) is not None
 
 
 def _is_positional_argument(
@@ -106,7 +112,9 @@ def _is_positional_argument(
                         inspect.Parameter.POSITIONAL_OR_KEYWORD)
     if parameter.kind not in positional_types:
         return False
-    return position == len(args)
+    if position == len(args):
+        return True
+    return position + 1 == len(args) and args[position] is None
 
 
 def _is_keyword_argument(parameter: inspect.Parameter) -> bool:

Inject should override value if None
When using the `@inject` decorator, the provided parameter should be overridden if it is `None`. At the moment the provider parameter takes precedence 100% of the time.
diff --git a/tests/test_container.py b/tests/test_container.py
index d76d2e1..f338f75 100644
--- a/tests/test_container.py
+++ b/tests/test_container.py
@@ -148,3 +148,29 @@ def test_injection_to_constructor():
     my_class = MyClass('my_test_string')
     assert my_class.some_str is 'my_test_string'
     assert my_class.get_val() is 1
+
+
+@provider('str_service')
+def provide_str():
+    return 'string service'
+
+
+def test_param_overriding():
+    @inject(string='str_service')
+    def my_fn(string):
+        return string
+
+    assert my_fn() == 'string service'
+    assert my_fn('overridden') == 'overridden'
+    assert my_fn(None) == 'string service'
+
+
+def test_multiple_param_overriding():
+    @inject(s1='str_service', s2='str_service')
+    def my_fn(s1, s2):
+        return s1, s2
+
+    assert my_fn() == ('string service', 'string service')
+    assert my_fn('overridden') == ('overridden', 'string service')
+    assert my_fn(None) == ('string service', 'string service')
+    assert my_fn('overridden', None) == ('overridden', 'string service')

pip install -e .[test]
parse_log_pytest
pytest
pytest
3.9
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
cachetools==5.5.2
chardet==5.2.0
colorama==0.4.6
coverage==7.8.0
distlib==0.3.9
docopt==0.6.2
exceptiongroup @ file:///croot/exceptiongroup_1706031385326/work
filelock==3.18.0
iniconfig @ file:///home/linux1/recipes/ci/iniconfig_1610983019677/work
-e git+https://github.com/jmwri/ioccontainer.git@9155dbf9030df7bd911a5bc93feb397d1f545feb#egg=ioccontainer
packaging @ file:///croot/packaging_1734472117206/work
platformdirs==4.3.7
pluggy @ file:///croot/pluggy_1733169602837/work
pyproject-api==1.9.0
pytest @ file:///croot/pytest_1738938843180/work
pytest-watch==4.2.0
tomli==2.2.1
tox==4.25.0
typing_extensions==4.13.0
virtualenv==20.29.3
watchdog==6.0.0

name: ioccontainer
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - exceptiongroup=1.2.0=py39h06a4308_0
  - iniconfig=1.1.1=pyhd3eb1b0_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.4.4=h6a678d5_1
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=3.0.16=h5eee18b_0
  - packaging=24.2=py39h06a4308_0
  - pip=25.0=py39h06a4308_0
  - pluggy=1.5.0=py39h06a4308_0
  - pytest=8.3.4=py39h06a4308_0
  - python=3.9.21=he870216_1
  - readline=8.2=h5eee18b_0
  - setuptools=75.8.0=py39h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - tzdata=2025a=h04d1e81_0
  - wheel=0.45.1=py39h06a4308_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - cachetools==5.5.2
      - chardet==5.2.0
      - colorama==0.4.6
      - coverage==7.8.0
      - distlib==0.3.9
      - docopt==0.6.2
      - filelock==3.18.0
      - platformdirs==4.3.7
      - pyproject-api==1.9.0
      - pytest-watch==4.2.0
      - tomli==2.2.1
      - tox==4.25.0
      - typing-extensions==4.13.0
      - virtualenv==20.29.3
      - watchdog==6.0.0
prefix: /opt/conda/envs/ioccontainer

tests/test_container.py::test_param_overriding tests/test_container.py::test_multiple_param_overriding
tests/test_container.py::test_injection tests/test_container.py::test_singleton tests/test_container.py::test_invalid_scope tests/test_container.py::test_duplicate_provider tests/test_container.py::test_invalid_provider tests/test_container.py::test_invalid_service_name tests/test_container.py::test_no_provider_specified tests/test_container.py::test_multiple_params tests/test_container.py::test_default_provided tests/test_container.py::test_argument_provided tests/test_container.py::test_threaded_provider tests/test_container.py::test_injection_to_constructor
ioccontainer/inject.py
ioccontainer/inject.py