diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 91872c42cd7e..a3b4b55d2e2e 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -305,11 +305,9 @@ poll_again:
 		break;
 	case 14: /* Down */
 	case 16: /* Up */
-		memset(tmpbuffer, ' ',
-		       strlen(kdb_prompt_str) + (lastchar-buffer));
-		*(tmpbuffer+strlen(kdb_prompt_str) +
-		  (lastchar-buffer)) = '\0';
-		kdb_printf("\r%s\r", tmpbuffer);
+		kdb_printf("\r%*c\r",
+			   (int)(strlen(kdb_prompt_str) + (lastchar - buffer)),
+			   ' ');
 		*lastchar = (char)key;
 		*(lastchar+1) = '\0';
 		return lastchar;