diff --git a/shlab/tsh.c b/shlab/tsh.c
index a5344ef..ee14e94 100644
--- a/shlab/tsh.c
+++ b/shlab/tsh.c
@@ -177,7 +177,7 @@ void eval(char *cmdline)
         return;
     }
     // run external command
-    if (!builtin_cmd(argv))
+    if (!builtin_cmd(argv)) // built-in command is done in `builtin_cmd`
     {
         if ((pid = fork()) == 0) // this is child
         {
@@ -267,6 +267,10 @@ int parseline(const char *cmdline, char **argv)
  */
 int builtin_cmd(char **argv) 
 {
+    if (strcmp(argv[0], "quit") == 0) // process quit command
+    {
+        exit(0);
+    }
     return 0;     /* not a builtin command */
 }