diff --git a/.github/workflows/tests.yaml b/.github/workflows/tests.yaml
index 685ed3a97b..b5bad323dc 100644
--- a/.github/workflows/tests.yaml
+++ b/.github/workflows/tests.yaml
@@ -104,7 +104,7 @@ jobs:
       - name: "Install packages"
         run: |
             sudo apt-get -y update
-            sudo apt-get -y --no-install-recommends install python3-behave diffstat diffutils python3 python3-cryptography python3-pip python3-rpm python3-setuptools python3-urllib3
+            sudo apt-get -y --no-install-recommends install python3-behave diffstat diffutils python3 python3-cryptography python3-pip python3-rpm python3-setuptools python3-typeguard python3-urllib3
 
       - name: "Checkout sources"
         uses: actions/checkout@v3
diff --git a/contrib/osc.spec b/contrib/osc.spec
index 95ef97aa1a..1a1e3eb354 100644
--- a/contrib/osc.spec
+++ b/contrib/osc.spec
@@ -30,6 +30,13 @@
 %bcond_with fdupes
 %endif
 
+# use typeguard during build on distros where typeguard is available
+%if (0%{?suse_version} > 1500 || 0%{?fedora} >= 37)
+%bcond_without typeguard
+%else
+%bcond_with typeguard
+%endif
+
 %define argparse_manpage_pkg argparse-manpage
 %define obs_build_pkg obs-build
 %define openssh_pkg openssh
@@ -68,6 +75,9 @@ BuildRequires:  %{use_python_pkg}-cryptography
 BuildRequires:  %{use_python_pkg}-devel >= 3.6
 BuildRequires:  %{use_python_pkg}-rpm
 BuildRequires:  %{use_python_pkg}-setuptools
+%if %{with typeguard}
+BuildRequires:  %{use_python_pkg}-typeguard
+%endif
 BuildRequires:  %{use_python_pkg}-urllib3
 BuildRequires:  diffstat
 %if %{with fdupes}
diff --git a/osc-wrapper.py b/osc-wrapper.py
index 952f69cf62..3411a4af5a 100755
--- a/osc-wrapper.py
+++ b/osc-wrapper.py
@@ -4,6 +4,28 @@
 This wrapper allows osc to be called from the source directory during development.
 """
 
+
+# developers and early adopters have typeguard enabled
+# so they can catch and report issues early
+try:
+    from typeguard import install_import_hook
+except ImportError:
+    install_import_hook = None
+
+if install_import_hook is None:
+    try:
+        from typeguard.importhook import install_import_hook
+    except ImportError:
+        install_import_hook = None
+
+if install_import_hook:
+    # install typeguard import hook only if available
+    install_import_hook("osc")
+else:
+    import osc.oscerr
+    raise osc.oscerr.PackageNotInstalled("python3-typeguard")
+
+
 import osc.babysitter
 
 osc.babysitter.main()
diff --git a/osc/commandline.py b/osc/commandline.py
index f488794e6d..1e8d027976 100644
--- a/osc/commandline.py
+++ b/osc/commandline.py
@@ -584,10 +584,10 @@ def pop_args(
     args,
     arg1_name: str = None,
     arg1_is_optional: bool = False,
-    arg1_default: str = None,
+    arg1_default: Optional[str] = None,
     arg2_name: str = None,
     arg2_is_optional: bool = False,
-    arg2_default: str = None,
+    arg2_default: Optional[str] = None,
 ):
     """
     Pop 2 arguments from `args`.
@@ -658,9 +658,9 @@ def pop_args(
 def pop_project_package_from_args(
     args: List[str],
     project_is_optional: bool = False,
-    default_project: str = None,
+    default_project: Optional[str] = None,
     package_is_optional: bool = False,
-    default_package: str = None,
+    default_package: Optional[str] = None,
 ):
     """
     Pop project and package from given `args`.
@@ -729,9 +729,9 @@ def pop_project_package_from_args(
 def pop_repository_arch_from_args(
     args: List[str],
     repository_is_optional: bool = False,
-    default_repository: str = None,
+    default_repository: Optional[str] = None,
     arch_is_optional: bool = False,
-    default_arch: str = None,
+    default_arch: Optional[str] = None,
 ):
     """
     Pop repository and arch from given `args`.
@@ -768,13 +768,13 @@ def pop_repository_arch_from_args(
 def pop_project_package_repository_arch_from_args(
     args: List[str],
     project_is_optional: bool = False,
-    default_project: str = None,
+    default_project: Optional[str] = None,
     package_is_optional: bool = False,
-    default_package: str = None,
+    default_package: Optional[str] = None,
     repository_is_optional: bool = False,
-    default_repository: str = None,
+    default_repository: Optional[str] = None,
     arch_is_optional: bool = False,
-    default_arch: str = None,
+    default_arch: Optional[str] = None,
 ):
     """
     Pop project, package, repository and arch from given `args`.
@@ -854,13 +854,13 @@ def pop_project_package_repository_arch_from_args(
 def pop_project_package_targetproject_targetpackage_from_args(
     args: List[str],
     project_is_optional: bool = False,
-    default_project: str = None,
+    default_project: Optional[str] = None,
     package_is_optional: bool = False,
-    default_package: str = None,
+    default_package: Optional[str] = None,
     target_project_is_optional: bool = False,
-    default_target_project: str = None,
+    default_target_project: Optional[str] = None,
     target_package_is_optional: bool = False,
-    default_target_package: str = None,
+    default_target_package: Optional[str] = None,
 ):
     """
     Pop project, package, target project and target package from given `args`.
diff --git a/osc/core.py b/osc/core.py
index a9bb3b6801..19809b44be 100644
--- a/osc/core.py
+++ b/osc/core.py
@@ -1192,7 +1192,7 @@ def __str__(self):
     @staticmethod
     def init_project(
         apiurl: str,
-        dir: Path,
+        dir: str,
         project,
         package_tracking=True,
         getPackageList=True,
@@ -2176,7 +2176,7 @@ def status(self, n):
 
         return state
 
-    def get_diff(self, revision=None, ignoreUnversioned=False):
+    def get_diff(self, revision: Optional[int] = None, ignoreUnversioned=False):
         diff_hdr = b'Index: %s\n'
         diff_hdr += b'===================================================================\n'
         kept = []
@@ -2274,7 +2274,7 @@ def diff_add_delete(fname, add, revision):
                 continue
             elif state == ' ' and revision is None:
                 continue
-            elif not revision_is_empty(revision) and self.findfilebyname(f.name).md5 == f.md5 and state != 'M':
+            elif not revision_is_empty(revision) and self.findfilebyname(f.name).md5 == f.md5 and state != "M":
                 continue
             yield [diff_hdr % f.name.encode()]
             if revision is None:
@@ -3739,7 +3739,7 @@ def meta_get_project_list(apiurl: str, deleted=False):
     return sorted(node.get('name') for node in root if node.get('name'))
 
 
-def show_project_meta(apiurl: str, prj: str, rev=None, blame=None):
+def show_project_meta(apiurl: str, prj: str, rev: Optional[int] = None, blame=None):
     query = {}
     if blame:
         query['view'] = "blame"
@@ -3766,7 +3766,7 @@ def show_project_meta(apiurl: str, prj: str, rev=None, blame=None):
     return f.readlines()
 
 
-def show_project_conf(apiurl: str, prj: str, rev=None, blame=None):
+def show_project_conf(apiurl: str, prj: str, rev: Optional[int] = None, blame=None):
     query = {}
     url = None
     if not revision_is_empty(rev):
@@ -4196,7 +4196,7 @@ def show_files_meta(
     apiurl: str,
     prj: str,
     pac: str,
-    revision=None,
+    revision: Optional[int] = None,
     expand=False,
     linkrev=None,
     linkrepair=False,
@@ -4843,7 +4843,7 @@ def get_request_collection(
     package=None,
     states=None,
     review_states=None,
-    types: List[str] = None,
+    types: Optional[List[str]] = None,
     ids=None,
     withfullhistory=False
 ):
@@ -5388,10 +5388,10 @@ def server_diff(
     apiurl: str,
     old_project: str,
     old_package: str,
-    old_revision: str,
+    old_revision: Optional[str],
     new_project: str,
     new_package: str,
-    new_revision: str,
+    new_revision: Optional[str],
     unified=False,
     missingok=False,
     meta=False,
@@ -5399,7 +5399,7 @@ def server_diff(
     onlyissues=False,
     full=True,
     xml=False,
-    files: list = None,
+    files: Optional[list] = None,
 ):
     query: Dict[str, Union[str, int]] = {"cmd": "diff"}
     if expand:
@@ -5454,17 +5454,17 @@ def server_diff_noex(
     apiurl: str,
     old_project: str,
     old_package: str,
-    old_revision: str,
+    old_revision: Optional[str],
     new_project: str,
     new_package: str,
-    new_revision: str,
+    new_revision: Optional[str],
     unified=False,
     missingok=False,
     meta=False,
     expand=True,
     onlyissues=False,
     xml=False,
-    files: list = None,
+    files: Optional[list] = None,
 ):
     try:
         return server_diff(apiurl,
@@ -7709,7 +7709,7 @@ def owner(
     return res
 
 
-def set_link_rev(apiurl: str, project: str, package: str, revision="", expand=False, msg: str=None):
+def set_link_rev(apiurl: str, project: str, package: str, revision="", expand=False, msg: Optional[str] = None):
     url = makeurl(apiurl, ["source", project, package, "_link"])
     try:
         f = http_GET(url)
diff --git a/setup.cfg b/setup.cfg
index 0987f75808..713aa2bb3f 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -42,6 +42,7 @@ install_requires =
     cryptography
     # rpm is not available on pip, install a matching package manually prior installing osc
     rpm
+    typeguard
     urllib3
 
 [options.extras_require]
diff --git a/tests/__init__.py b/tests/__init__.py
index e69de29bb2..2740d5773f 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -0,0 +1,14 @@
+try:
+    from typeguard import install_import_hook
+except ImportError:
+    install_import_hook = None
+
+if not install_import_hook:
+    try:
+        from typeguard.importhook import install_import_hook
+    except ImportError:
+        install_import_hook = None
+
+if install_import_hook:
+    # install typeguard import hook only if available
+    install_import_hook("osc")