diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index fab3111..a440af8 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -1797,6 +1797,7 @@ hammer_time(u_int64_t modulep, u_int64_t physfree)
 	/* setup proc 0's pcb */
 	thread0.td_pcb->pcb_flags = 0;
 	thread0.td_pcb->pcb_cr3 = KPML4phys;
+	thread0.td_pcb->pcb_signature = PCB_SIGNATURE;
 	thread0.td_frame = &proc0_tf;
 
         env = getenv("kernelname");
diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
index f7c0d2d..3f91156 100644
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -1405,6 +1405,28 @@ void
 pmap_qremove(vm_offset_t sva, int count)
 {
 	vm_offset_t va;
+	struct pcb *pcb;
+	int i;
+
+	for (i = 1; i <= count; i++) {
+		pcb = (struct pcb *)(sva + i * PAGE_SIZE - sizeof(struct pcb));
+		if (pcb->pcb_signature == PCB_SIGNATURE)
+			panic("pmap_qremove pcb");
+	}
+
+	va = sva;
+	while (count-- > 0) {
+		pmap_kremove(va);
+		va += PAGE_SIZE;
+	}
+	pmap_invalidate_range(kernel_pmap, sva, va);
+}
+
+void pmap_qremove_stack(vm_offset_t sva, int count);
+void
+pmap_qremove_stack(vm_offset_t sva, int count)
+{
+	vm_offset_t va;
 
 	va = sva;
 	while (count-- > 0) {
diff --git a/sys/amd64/include/pcb.h b/sys/amd64/include/pcb.h
index 1af8f6d..1ba529f 100644
--- a/sys/amd64/include/pcb.h
+++ b/sys/amd64/include/pcb.h
@@ -43,7 +43,9 @@
 #include <machine/fpu.h>
 #include <machine/segments.h>
 
+#define PCB_SIGNATURE	0xdead10235201cafe
 struct pcb {
+	register_t	pcb_signature;
 	register_t	pcb_r15;
 	register_t	pcb_r14;
 	register_t	pcb_r13;
diff --git a/sys/vm/vm_glue.c b/sys/vm/vm_glue.c
index c552cb7..10c8123 100644
--- a/sys/vm/vm_glue.c
+++ b/sys/vm/vm_glue.c
@@ -95,6 +95,8 @@ __FBSDID("$FreeBSD$");
 #include <vm/vm_pager.h>
 #include <vm/swap_pager.h>
 
+void pmap_qremove_stack(vm_offset_t sva, int count);
+
 /*
  * System initialization
  *
@@ -411,7 +413,7 @@ vm_thread_new(struct thread *td, int pages)
 
 	atomic_add_int(&kstacks, 1);
 	if (KSTACK_GUARD_PAGES != 0) {
-		pmap_qremove(ks, KSTACK_GUARD_PAGES);
+		pmap_qremove_stack(ks, KSTACK_GUARD_PAGES);
 		ks += KSTACK_GUARD_PAGES * PAGE_SIZE;
 	}
 	td->td_kstack_obj = ksobj;
@@ -447,7 +449,7 @@ vm_thread_stack_dispose(vm_object_t ksobj, vm_offset_t ks, int pages)
 	int i;
 
 	atomic_add_int(&kstacks, -1);
-	pmap_qremove(ks, pages);
+	pmap_qremove_stack(ks, pages);
 	VM_OBJECT_LOCK(ksobj);
 	for (i = 0; i < pages; i++) {
 		m = vm_page_lookup(ksobj, i);
@@ -536,7 +538,7 @@ vm_thread_swapout(struct thread *td)
 	cpu_thread_swapout(td);
 	pages = td->td_kstack_pages;
 	ksobj = td->td_kstack_obj;
-	pmap_qremove(td->td_kstack, pages);
+	pmap_qremove_stack(td->td_kstack, pages);
 	VM_OBJECT_LOCK(ksobj);
 	for (i = 0; i < pages; i++) {
 		m = vm_page_lookup(ksobj, i);