diff --git a/src/rosbags/serde/utils.py b/src/rosbags/serde/utils.py
index 15362b23..7ee18e49 100644
--- a/src/rosbags/serde/utils.py
+++ b/src/rosbags/serde/utils.py
@@ -98,6 +98,8 @@ def compile_lines(lines: List[str]) -> ModuleType:
         Compiled and loaded module.
 
     """
-    module = module_from_spec(spec_from_loader('tmpmod', loader=None))
+    spec = spec_from_loader('tmpmod', loader=None)
+    assert spec
+    module = module_from_spec(spec)
     exec('\n'.join(lines), module.__dict__)  # pylint: disable=exec-used
     return module
diff --git a/src/rosbags/typesys/register.py b/src/rosbags/typesys/register.py
index 4a4b07af..875f930e 100644
--- a/src/rosbags/typesys/register.py
+++ b/src/rosbags/typesys/register.py
@@ -92,6 +92,7 @@ def register_types(typs: Typesdict) -> None:
     code = generate_python_code(typs)
     name = 'rosbags.usertypes'
     spec = spec_from_loader(name, loader=None)
+    assert spec
     module = module_from_spec(spec)
     sys.modules[name] = module
     exec(code, module.__dict__)  # pylint: disable=exec-used