diff --git a/kernel/memlayout.h b/kernel/memlayout.h
index 13d1705..ef5c1e1 100644
--- a/kernel/memlayout.h
+++ b/kernel/memlayout.h
@@ -53,4 +53,4 @@
 // map the trampoline page to the highest address,
 // in both user and kernel space.
 #define TRAMPOLINE (MAXVA - PGSIZE)
-#define KSTACK(p) ((TRAMPOLINE-PGSIZE)-p*2*PGSIZE)
+#define KSTACK(p) (TRAMPOLINE - (p+1)* 2*PGSIZE)