diff --git a/src/os_ops.py b/src/os_ops.py
index c7d235c..fbaa351 100644
--- a/src/os_ops.py
+++ b/src/os_ops.py
@@ -106,7 +106,7 @@ def exec_command(
         assert type(get_process) is bool
         assert type(ignore_errors) is bool
         assert exec_env is None or type(exec_env) is dict
-        assert cwd is None or type(cwd) is dict
+        assert cwd is None or type(cwd) is str
         RaiseError.MethodIsNotImplemented(__class__, "exec_command")
 
     def build_path(self, a: str, *parts: str) -> str: