diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 370c89b..6f8f660 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -6,6 +6,11 @@
 
 static void syscall_handler (struct intr_frame *);
 
+/* A syscall_function is a function that receives up to 3 arguments, the
+   arguments to the functions are either ints or pointers taking up to 32 bits
+   in size. */
+typedef uintptr_t syscall_function (uintptr_t, uintptr_t, uintptr_t);
+
 void
 syscall_init (void) 
 {