diff --git a/sys/amd64/amd64/support.S b/sys/amd64/amd64/support.S
index ea547f90973..4e8efdfa590 100644
--- a/sys/amd64/amd64/support.S
+++ b/sys/amd64/amd64/support.S
@@ -313,6 +313,34 @@ copyin_fault:
 	movq	$EFAULT,%rax
 	ret
 
+/*
+ * casuword32.  Compare and set user integer.  Returns -1 or the current value.
+ *        dst = %rdi, old = %rsi, new = %rdx
+ */
+ENTRY(casuword32)
+	movq	PCPU(CURPCB),%rcx
+	movq	$fusufault,PCB_ONFAULT(%rcx)
+
+	movq	$VM_MAXUSER_ADDRESS-4,%rax
+	cmpq	%rax,%rdi			/* verify address is valid */
+	ja	fusufault
+
+	movl	%esi,%eax			/* old */
+#ifdef SMP
+	lock
+#endif
+	cmpxchgl %edx,(%rdi)			/* new = %edx */
+
+	/*
+	 * The old value is in %eax.  If the store succeeded it will be the
+	 * value we expected (old) from before the store, otherwise it will
+	 * be the current value.
+	 */
+
+	movq	PCPU(CURPCB),%rcx
+	movq	$0,PCB_ONFAULT(%rcx)
+	ret
+
 /*
  * casuptr.  Compare and set user pointer.  Returns -1 or the current value.
  *        dst = %rdi, old = %rsi, new = %rdx
diff --git a/sys/arm/arm/fusu.S b/sys/arm/arm/fusu.S
index 095491aa96a..f0d3688bb9f 100644
--- a/sys/arm/arm/fusu.S
+++ b/sys/arm/arm/fusu.S
@@ -52,6 +52,7 @@ __FBSDID("$FreeBSD$");
  * Fetch an int from the user's address space.
  */
 
+ALTENTRY(casuword32)
 ENTRY(casuptr)
 #ifdef MULTIPROCESSOR
 	/* XXX Probably not appropriate for non-Hydra SMPs */
diff --git a/sys/i386/i386/support.s b/sys/i386/i386/support.s
index c3ac1731401..aee43a4f02a 100644
--- a/sys/i386/i386/support.s
+++ b/sys/i386/i386/support.s
@@ -1142,6 +1142,8 @@ fastmove_tail_fault:
 /*
  * casuptr.  Compare and set user pointer.  Returns -1 or the current value.
  */
+
+ALTENTRY(casuword32)
 ENTRY(casuptr)
 	movl	PCPU(CURPCB),%ecx
 	movl	$fusufault,PCB_ONFAULT(%ecx)
diff --git a/sys/ia64/ia64/support.S b/sys/ia64/ia64/support.S
index 95686b34bcb..4a212747307 100644
--- a/sys/ia64/ia64/support.S
+++ b/sys/ia64/ia64/support.S
@@ -241,6 +241,56 @@ ENTRY(casuptr, 3)
 }
 END(casuptr)
 
+/*
+ * casuword32(int32_t *p, int32_t old, int32_t new)
+ *	Perform a 32-bit compare-exchange in user space.
+ */
+ENTRY(casuword32, 3)
+{	.mlx
+	add		r15=PC_CURTHREAD,r13
+	movl		r14=VM_MAX_ADDRESS
+	;;
+}
+{	.mib
+	ld8		r15=[r15]		// r15 = curthread
+	cmp.geu		p6,p0=in0,r14
+(p6)	br.dpnt.few	1f
+	;;
+}
+{	.mlx
+	add		r15=TD_PCB,r15
+	movl		r14=fusufault
+	;;
+}
+{	.mmi
+	ld8		r15=[r15]		// r15 = PCB
+	;;
+	mov		ar.ccv=in1
+	add		r15=PCB_ONFAULT,r15
+	;;
+}
+{	.mmi
+	st8		[r15]=r14		// Set onfault
+	;;
+	cmpxchg4.rel	ret0=[in0],in2,ar.ccv
+	nop		0
+	;;
+}
+{	.mfb
+	st8.rel		[r15]=r0		// Clear onfault
+	nop		0
+	br.ret.sptk	rp
+	;;
+}
+1:
+{	.mfb
+	add		ret0=-1,r0
+	nop		0
+	br.ret.sptk	rp
+	;;
+}
+END(casuword32)
+
 /*
  * subyte(void *addr, int byte)
  * suword16(void *addr, int word)
diff --git a/sys/powerpc/aim/copyinout.c b/sys/powerpc/aim/copyinout.c
index 7fa91ceaaf1..4c19cbfe925 100644
--- a/sys/powerpc/aim/copyinout.c
+++ b/sys/powerpc/aim/copyinout.c
@@ -322,6 +322,12 @@ fuword32(const void *addr)
 	return ((int32_t)fuword(addr));
 }
 
+int32_t
+casuword32(int32_t *base, int32_t oldval, int32_t newval)
+{
+	return (casuptr(base, oldval, newval));
+}
+
 intptr_t
 casuptr(intptr_t *addr, intptr_t old, intptr_t new)
 {
diff --git a/sys/powerpc/powerpc/copyinout.c b/sys/powerpc/powerpc/copyinout.c
index 7fa91ceaaf1..4c19cbfe925 100644
--- a/sys/powerpc/powerpc/copyinout.c
+++ b/sys/powerpc/powerpc/copyinout.c
@@ -322,6 +322,12 @@ fuword32(const void *addr)
 	return ((int32_t)fuword(addr));
 }
 
+int32_t
+casuword32(int32_t *base, int32_t oldval, int32_t newval)
+{
+	return (casuptr(base, oldval, newval));
+}
+
 intptr_t
 casuptr(intptr_t *addr, intptr_t old, intptr_t new)
 {
diff --git a/sys/sparc64/sparc64/support.S b/sys/sparc64/sparc64/support.S
index 57ca6379242..d554f63f796 100644
--- a/sys/sparc64/sparc64/support.S
+++ b/sys/sparc64/sparc64/support.S
@@ -402,7 +402,7 @@ fs_nofault_begin:
 	.set	susword, suword16
 	.set	suword, suword64
 
-	.globl	casuptr, fuptr, suptr
+	.globl	casuword32, casuptr, fuptr, suptr
 	.set	casuptr, casuword64
 	.set	fuptr, fuword64
 	.set	suptr, suword64
diff --git a/sys/sys/systm.h b/sys/sys/systm.h
index 35872f4a84e..bc2c65d7c5b 100644
--- a/sys/sys/systm.h
+++ b/sys/sys/systm.h
@@ -203,7 +203,8 @@ int	suword(void *base, long word);
 int	suword16(void *base, int word);
 int	suword32(void *base, int32_t word);
 int	suword64(void *base, int64_t word);
-intptr_t casuptr(intptr_t *p, intptr_t old, intptr_t new);
+int32_t	casuword32(int32_t *base, int32_t oldval, int32_t newval);
+intptr_t casuptr(intptr_t *p, intptr_t oldval, intptr_t newval);
 
 void	realitexpire(void *);