diff --git a/sys/arm/arm/genassym.c b/sys/arm/arm/genassym.c
index 6f940328d9cd..ab0be4ca138d 100644
--- a/sys/arm/arm/genassym.c
+++ b/sys/arm/arm/genassym.c
@@ -60,7 +60,6 @@ ASSYM(PCB_NOALIGNFLT, PCB_NOALIGNFLT);
 ASSYM(PCB_ONFAULT, offsetof(struct pcb, pcb_onfault));
 ASSYM(PCB_DACR, offsetof(struct pcb, pcb_dacr));
 ASSYM(PCB_FLAGS, offsetof(struct pcb, pcb_flags));
-ASSYM(PCB_UND_SP, offsetof(struct pcb, un_32.pcb32_und_sp));
 ASSYM(PCB_PAGEDIR, offsetof(struct pcb, pcb_pagedir));
 ASSYM(PCB_L1VEC, offsetof(struct pcb, pcb_l1vec));
 ASSYM(PCB_PL1VEC, offsetof(struct pcb, pcb_pl1vec));
diff --git a/sys/arm/arm/machdep.c b/sys/arm/arm/machdep.c
index 35f14326e352..289f2536631e 100644
--- a/sys/arm/arm/machdep.c
+++ b/sys/arm/arm/machdep.c
@@ -379,8 +379,6 @@ cpu_startup(void *dummy)
 
 	bufinit();
 	vm_pager_bufferinit();
-	pcb->un_32.pcb32_und_sp = (u_int)thread0.td_kstack +
-	    USPACE_UNDEF_STACK_TOP;
 	pcb->un_32.pcb32_sp = (u_int)thread0.td_kstack +
 	    USPACE_SVC_STACK_TOP;
 	vector_page_setprot(VM_PROT_READ);
diff --git a/sys/arm/arm/swtch.S b/sys/arm/arm/swtch.S
index 743d4c35d5fb..2703b035d044 100644
--- a/sys/arm/arm/swtch.S
+++ b/sys/arm/arm/swtch.S
@@ -303,17 +303,6 @@ ENTRY(cpu_switch)
 	/* Get the user structure for the new process in r9 */
 	ldr	r9, [r1, #(TD_PCB)]
 
-        mrs	r3, cpsr
-	/*
-	 * We can do that, since
-	 * PSR_SVC32_MODE|PSR_UND32_MODE == MSR_UND32_MODE
-	 */
-	orr	r8, r3, #(PSR_UND32_MODE)
-        msr	cpsr_c, r8
-
-	str	sp, [r2, #(PCB_UND_SP)]
-
-        msr	cpsr_c, r3		/* Restore the old mode */
 	/* rem: r2 = old PCB */
 	/* rem: r9 = new PCB */
 	/* rem: interrupts are enabled */
@@ -422,10 +411,6 @@ ENTRY(cpu_switch)
 	movne	r0, #0			/* We *know* vector_page's VA is 0x0 */
 	movne	lr, pc
 	ldrne	pc, [r10, #CF_TLB_FLUSHID_SE]
-	/*
-	 * We can do that, since
-	 * PSR_SVC32_MODE|PSR_UND32_MODE == MSR_UND32_MODE
-	 */
 
 .Lcs_context_switched:
 
@@ -444,17 +429,6 @@ ENTRY(cpu_switch)
 
 	/* rem: r9 = new PCB */
 
-        mrs	r3, cpsr
-	/*
-	 * We can do that, since
-	 * PSR_SVC32_MODE|PSR_UND32_MODE == MSR_UND32_MODE
-	 */
-	orr	r2, r3, #(PSR_UND32_MODE)
-	msr	cpsr_c, r2
-
-	ldr	sp, [r9, #(PCB_UND_SP)]
-
-        msr	cpsr_c, r3		/* Restore the old mode */
 	/* Restore all the save registers */
 #ifndef _ARM_ARCH_5E
 	add	r7, r9, #PCB_R8
diff --git a/sys/arm/arm/vm_machdep.c b/sys/arm/arm/vm_machdep.c
index c51ae56f5585..8e177209a491 100644
--- a/sys/arm/arm/vm_machdep.c
+++ b/sys/arm/arm/vm_machdep.c
@@ -144,7 +144,6 @@ cpu_fork(register struct thread *td1, register struct proc *p2,
 	bcopy(td1->td_pcb, pcb2, sizeof(*pcb2));
 	mdp2 = &p2->p_md;
 	bcopy(&td1->td_proc->p_md, mdp2, sizeof(*mdp2));
-	pcb2->un_32.pcb32_und_sp = td2->td_kstack + USPACE_UNDEF_STACK_TOP;
 	pcb2->un_32.pcb32_sp = td2->td_kstack +
 	    USPACE_SVC_STACK_TOP - sizeof(*pcb2);
 	pmap_activate(td2);
@@ -366,7 +365,6 @@ cpu_set_upcall(struct thread *td, struct thread *td0)
 	tf->tf_spsr &= ~PSR_C_bit;
 	tf->tf_r0 = 0;
 	td->td_pcb->un_32.pcb32_sp = (u_int)sf;
-	td->td_pcb->un_32.pcb32_und_sp = td->td_kstack + USPACE_UNDEF_STACK_TOP;
 	KASSERT((td->td_pcb->un_32.pcb32_sp & 7) == 0,
 	    ("cpu_set_upcall: Incorrect stack alignment"));
 
diff --git a/sys/arm/include/param.h b/sys/arm/include/param.h
index 15fc2793798c..5cd0b7bb9187 100644
--- a/sys/arm/include/param.h
+++ b/sys/arm/include/param.h
@@ -125,10 +125,8 @@
 #define KSTACK_GUARD_PAGES	1
 #endif /* !KSTACK_GUARD_PAGES */
 
-#define USPACE_SVC_STACK_TOP		KSTACK_PAGES * PAGE_SIZE
-#define USPACE_SVC_STACK_BOTTOM		(USPACE_SVC_STACK_TOP - 0x1000)
-#define USPACE_UNDEF_STACK_TOP		(USPACE_SVC_STACK_BOTTOM - 0x10)
-#define USPACE_UNDEF_STACK_BOTTOM	(FPCONTEXTSIZE + 10)
+#define USPACE_SVC_STACK_TOP		(KSTACK_PAGES * PAGE_SIZE)
+
 /*
  * Mach derived conversion macros
  */
diff --git a/sys/arm/include/pcb.h b/sys/arm/include/pcb.h
index 8d98f2efa0e8..252d94e4522d 100644
--- a/sys/arm/include/pcb.h
+++ b/sys/arm/include/pcb.h
@@ -61,7 +61,6 @@ struct pcb_arm32 {
 	u_int	pcb32_sp;			/* used */
 	u_int	pcb32_lr;
 	u_int	pcb32_pc;
-	u_int	pcb32_und_sp;
 };
 #define	pcb_pagedir	un_32.pcb32_pagedir
 #define	pcb_pl1vec	un_32.pcb32_pl1vec