diff --git a/sys/src/9/pc64/main.c b/sys/src/9/pc64/main.c
index 479141637..e61840ea0 100644
--- a/sys/src/9/pc64/main.c
+++ b/sys/src/9/pc64/main.c
@@ -398,7 +398,7 @@ reboot(void *entry, void *code, ulong size)
 	/* shutdown devices */
 	chandevshutdown();
 
-	rebootjump((uintptr)entry & -0x10000000, PADDR(code), size);
+	rebootjump((uintptr)entry & (ulong)~0xF0000000UL, PADDR(code), size);
 }
 
 /*