diff --git a/userprog/syscall_write.c b/userprog/syscall_write.c
index 9c356db50727391fd00e5e6fa8e2837251227c54..525e2cfea8e17fc6804093b534dff982336adbf9 100644
--- a/userprog/syscall_write.c
+++ b/userprog/syscall_write.c
@@ -21,7 +21,10 @@ void syscall_write(struct intr_frame *f) {
     unsigned size = *((unsigned*)((int*)f->esp + 3)); // size to write is fourth
     // writing to stdout or stderr (fd in {1, 2}) is a special case
     switch (fd) {
-    case 1: // stdin
+    case 0: // writing to stdin (keyboard) is an error condition
+        f->eax = 0;
+        break;
+    case 1: // stdout
     case 2: // stderr
         write_to_console((const char*)buffer, size);
         f->eax = size;