diff --git a/spin/cmds/util.py b/spin/cmds/util.py
index e0ca361..f79dae3 100644
--- a/spin/cmds/util.py
+++ b/spin/cmds/util.py
@@ -170,9 +170,15 @@ def parent_cmd(*user_args, **user_kwargs):
         my_cmd.callback = click.pass_context(callback_with_parent_callback)
         my_cmd.callback._parent = user_func  # type: ignore[attr-defined]
 
+        # If doc is present then combine it with user_func.__doc__
+        # Otherwise override it with user_func.__doc__
+        # if it is not empty.
         if doc is not None:
-            my_cmd.help = doc
-        my_cmd.help = (my_cmd.help or "") + "\n\n" + (user_func.__doc__ or "")
+            my_cmd.help = doc + "\n\n" + (user_func.__doc__ or "")
+        else:
+            my_cmd.help = (my_cmd.help or "")
+            if user_func.__doc__ is not None:
+                my_cmd.help = user_func.__doc__
         my_cmd.help = my_cmd.help.strip()
 
         my_cmd.name = user_func.__name__.replace("_", "-")
diff --git a/spin/tests/test_extend_command.py b/spin/tests/test_extend_command.py
index 9677e9f..547e8c8 100644
--- a/spin/tests/test_extend_command.py
+++ b/spin/tests/test_extend_command.py
@@ -28,6 +28,7 @@ def build_ext(*, parent_callback, extra=None, **kwargs):
 
     assert "Additional docstring" in get_usage(build_ext)
     assert "Additional docstring" not in get_usage(cmds.meson.build)
+    assert get_usage(cmds.meson.build) not in get_usage(build_ext)
 
     @extend_command(cmds.meson.build, doc="Hello world")
     def build_ext(*, parent_callback, extra=None, **kwargs):
@@ -39,6 +40,7 @@ def build_ext(*, parent_callback, extra=None, **kwargs):
     doc = get_usage(build_ext)
     assert "Hello world\n" in doc
     assert "\n  Additional docstring" in doc
+    assert get_usage(cmds.meson.build) not in get_usage(build_ext)
 
 
 def test_ext_additional_args():