diff --git a/src/os_ops.py b/src/os_ops.py
index 8600237..c7d235c 100644
--- a/src/os_ops.py
+++ b/src/os_ops.py
@@ -132,7 +132,7 @@ def environ(self, var_name: str) -> typing.Optional[str]:
         assert var_name != ""
         RaiseError.MethodIsNotImplemented(__class__, "environ")
 
-    def cwd(self):
+    def cwd(self) -> str:
         RaiseError.MethodIsNotImplemented(__class__, "cwd")
 
     def find_executable(self, executable: str) -> typing.Optional[str]:
diff --git a/src/remote_ops.py b/src/remote_ops.py
index 40c1a43..ffadc8a 100644
--- a/src/remote_ops.py
+++ b/src/remote_ops.py
@@ -347,7 +347,7 @@ def environ(self, var_name: str) -> typing.Optional[str]:
             out=stdout,
         )
 
-    def cwd(self):
+    def cwd(self) -> str:
         cmd = 'pwd'
         stdout = self.exec_command(cmd, encoding=get_default_encoding())
         assert type(stdout) is str