diff --git a/nshlib/nsh_command.c b/nshlib/nsh_command.c
index 213e70732..a251c1af9 100644
--- a/nshlib/nsh_command.c
+++ b/nshlib/nsh_command.c
@@ -218,7 +218,7 @@ static const struct cmdmap_s g_cmdmap[] =
 
 #ifdef CONFIG_DEBUG_MM
 # ifndef CONFIG_NSH_DISABLE_MEMDUMP
-  { "memdump",  cmd_memdump,  1, 3, "[pid/used/free]" },
+  { "memdump",  cmd_memdump,  1, 3, "[pid/used/free/on/off]" },
 # endif
 #endif