diff --git a/osbuild/main_cli.py b/osbuild/main_cli.py
index 88cfdd84..1bbb70f9 100644
--- a/osbuild/main_cli.py
+++ b/osbuild/main_cli.py
@@ -95,7 +95,7 @@ def parse_arguments(sys_argv):
 
 
 # pylint: disable=too-many-branches
-def osbuild_cli(*, sys_argv=[]):
+def osbuild_cli(*, sys_argv):
     args = parse_arguments(sys_argv)
     manifest = parse_manifest(args.manifest_path)
 
diff --git a/osbuild/meta.py b/osbuild/meta.py
index c0edd0a6..25495b15 100644
--- a/osbuild/meta.py
+++ b/osbuild/meta.py
@@ -128,7 +128,7 @@ class ValidationResult:
         self.errors.add(err)
         return self
 
-    def merge(self, result: "ValidationResult", *, path=[]):
+    def merge(self, result: "ValidationResult", *, path=None):
         """Merge all errors of `result` into this
 
         Merge all the errors of in `result` into this,
@@ -137,7 +137,7 @@ class ValidationResult:
         """
         for err in result:
             err = copy.deepcopy(err)
-            err.rebase(path)
+            err.rebase(path or [])
             self.errors.add(err)
 
     def as_dict(self):
diff --git a/osbuild/util/jsoncomm.py b/osbuild/util/jsoncomm.py
index 1591642b..500e8d41 100644
--- a/osbuild/util/jsoncomm.py
+++ b/osbuild/util/jsoncomm.py
@@ -271,7 +271,7 @@ class Socket(contextlib.AbstractContextManager):
 
         return (payload, fdset, msg[3])
 
-    def send(self, payload: object, *, destination: Optional[str] = None, fds: list = []):
+    def send(self, payload: object, *, destination: Optional[str] = None, fds: Optional[list] = None):
         """Send Message
 
         Send a new message via this socket. This operation is synchronous. The
@@ -299,7 +299,7 @@ class Socket(contextlib.AbstractContextManager):
 
         serialized = json.dumps(payload).encode()
         cmsg = []
-        if len(fds) > 0:
+        if fds and len(fds) > 0:
             cmsg.append((socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds)))
 
         n = self._socket.sendmsg([serialized], cmsg, 0, destination)
diff --git a/test/test.py b/test/test.py
index 8b1da354..8bc9457d 100644
--- a/test/test.py
+++ b/test/test.py
@@ -227,7 +227,7 @@ class OSBuild(contextlib.AbstractContextManager):
         print(data_stderr)
         print("-- END ---------------------------------")
 
-    def compile(self, data_stdin, checkpoints=[]):
+    def compile(self, data_stdin, checkpoints=None):
         """Compile an Artifact
 
         This takes a manifest as `data_stdin`, executes the pipeline, and
@@ -247,7 +247,7 @@ class OSBuild(contextlib.AbstractContextManager):
         cmd_args += ["--output-directory", self._outputdir]
         cmd_args += ["--store", self._cachedir]
 
-        for c in checkpoints:
+        for c in (checkpoints or []):
             cmd_args += ["--checkpoint", c]
 
         # Spawn the `osbuild` executable, feed it the specified data on
@@ -272,7 +272,7 @@ class OSBuild(contextlib.AbstractContextManager):
             self._print_result(p.returncode, data_stdout, data_stderr)
             self._unittest.assertEqual(p.returncode, 0)
 
-    def compile_file(self, file_stdin, checkpoints=[]):
+    def compile_file(self, file_stdin, checkpoints=None):
         """Compile an Artifact
 
         This is similar to `compile()` but takes a file-path instead of raw