diff --git a/exec.c b/exec.c
index e5d1816..d56ee1d 100644
--- a/exec.c
+++ b/exec.c
@@ -44,6 +44,8 @@ exec(char *path, char **argv)
       continue;
     if(ph.memsz < ph.filesz)
       goto bad;
+    if(ph.vaddr + ph.memsz < ph.vaddr)
+      goto bad;
     if((sz = allocuvm(pgdir, sz, ph.vaddr + ph.memsz)) == 0)
       goto bad;
     if(ph.vaddr % PGSIZE != 0)