diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 401559370b3..9290a6a7757 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -241,6 +241,11 @@ vm_page_startup(vm_offset_t starta, vm_offset_t enda, vm_offset_t vaddr)
 	    (end - new_end)) / PAGE_SIZE;
 	end = new_end;
 
+	/*
+	 * Reserve an unmapped guard page to trap access to vm_page_array[-1].
+	 */
+	vaddr += PAGE_SIZE;
+
 	/*
 	 * Initialize the mem entry structures now, and put them in the free
 	 * queue.