-This mode arranges for \"saving\" this buffer to write the data
-into the tar-file buffer that it came from. The changes will actually
-appear on disk when you save the tar-file's buffer."
+With a prefix argument ARG, enable the mode if ARG is positive,
+and disable it otherwise. If called from Lisp, enable the mode
+if ARG is omitted or nil. This mode arranges for \"saving\" this
+buffer to write the data into the tar-file buffer that it came
+from. The changes will actually appear on disk when you save the
+tar-file's buffer."