diff --git a/userprog/system_calls.h b/userprog/system_calls.h
index 1d56a93e4767fdde504892f2d601684463945baa..235183330ee8f1944802728f29ee55337667f6d0 100644
--- a/userprog/system_calls.h
+++ b/userprog/system_calls.h
@@ -44,9 +44,10 @@ void syscall_create(struct intr_frame *f);
 void syscall_write(struct intr_frame *f);
 
 /*
- * NOTE: There are more system calls implemented by Pintos but we are not
- * implementing them because the assignment brief does not ask of it.
+ * Opens the file called file. Returns a nonnegative integer handle called a
+ * "file descriptor" (fd), or -1 if the file could not be opened.
  */
+void syscall_open(struct intr_frame *f);
 
 /*
  * special additional stuff for handling file descriptors because they're annoying