diff --git a/src/runtime/asm_386.s b/src/runtime/asm_386.s
index 40b5c2e0104..43f92b2b8b7 100644
--- a/src/runtime/asm_386.s
+++ b/src/runtime/asm_386.s
@@ -439,12 +439,7 @@ TEXT runtime·cas(SB), NOSPLIT, $0-13
 	MOVL	new+8(FP), CX
 	LOCK
 	CMPXCHGL	CX, 0(BX)
-	JZ 4(PC)
-	MOVL	$0, AX
-	MOVB	AX, ret+12(FP)
-	RET
-	MOVL	$1, AX
-	MOVB	AX, ret+12(FP)
+	SETEQ	, ret+12(FP)
 	RET
 
 TEXT runtime·casuintptr(SB), NOSPLIT, $0-13
@@ -475,13 +470,7 @@ TEXT runtime·cas64(SB), NOSPLIT, $0-21
 	MOVL	new_hi+16(FP), CX
 	LOCK
 	CMPXCHG8B	0(BP)
-	JNZ	fail
-	MOVL	$1, AX
-	MOVB	AX, ret+20(FP)
-	RET
-fail:
-	MOVL	$0, AX
-	MOVB	AX, ret+20(FP)
+	SETEQ	, ret+20(FP)
 	RET
 
 // bool casp(void **p, void *old, void *new)
@@ -497,12 +486,7 @@ TEXT runtime·casp1(SB), NOSPLIT, $0-13
 	MOVL	new+8(FP), CX
 	LOCK
 	CMPXCHGL	CX, 0(BX)
-	JZ 4(PC)
-	MOVL	$0, AX
-	MOVB	AX, ret+12(FP)
-	RET
-	MOVL	$1, AX
-	MOVB	AX, ret+12(FP)
+	SETEQ	, ret+12(FP)
 	RET
 
 // uint32 xadd(uint32 volatile *val, int32 delta)
diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index 3d96d090141..4061e99c4ba 100644
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -427,12 +427,7 @@ TEXT runtime·cas(SB), NOSPLIT, $0-17
 	MOVL	new+12(FP), CX
 	LOCK
 	CMPXCHGL	CX, 0(BX)
-	JZ 4(PC)
-	MOVL	$0, AX
-	MOVB	AX, ret+16(FP)
-	RET
-	MOVL	$1, AX
-	MOVB	AX, ret+16(FP)
+	SETEQ	, ret+16(FP)
 	RET
 
 // bool	runtime·cas64(uint64 *val, uint64 old, uint64 new)
@@ -449,13 +444,7 @@ TEXT runtime·cas64(SB), NOSPLIT, $0-25
 	MOVQ	new+16(FP), CX
 	LOCK
 	CMPXCHGQ	CX, 0(BX)
-	JNZ	fail
-	MOVL	$1, AX
-	MOVB	AX, ret+24(FP)
-	RET
-fail:
-	MOVL	$0, AX
-	MOVB	AX, ret+24(FP)
+	SETEQ	, ret+24(FP)
 	RET
 	
 TEXT runtime·casuintptr(SB), NOSPLIT, $0-25
@@ -483,12 +472,7 @@ TEXT runtime·casp1(SB), NOSPLIT, $0-25
 	MOVQ	new+16(FP), CX
 	LOCK
 	CMPXCHGQ	CX, 0(BX)
-	JZ 4(PC)
-	MOVL	$0, AX
-	MOVB	AX, ret+24(FP)
-	RET
-	MOVL	$1, AX
-	MOVB	AX, ret+24(FP)
+	SETEQ	, ret+24(FP)
 	RET
 
 // uint32 xadd(uint32 volatile *val, int32 delta)
diff --git a/src/runtime/asm_amd64p32.s b/src/runtime/asm_amd64p32.s
index 6a8544ed453..b9197347706 100644
--- a/src/runtime/asm_amd64p32.s
+++ b/src/runtime/asm_amd64p32.s
@@ -400,12 +400,7 @@ TEXT runtime·cas(SB), NOSPLIT, $0-17
 	MOVL	new+8(FP), CX
 	LOCK
 	CMPXCHGL	CX, 0(BX)
-	JZ 4(PC)
-	MOVL	$0, AX
-	MOVB	AX, ret+16(FP)
-	RET
-	MOVL	$1, AX
-	MOVB	AX, ret+16(FP)
+	SETEQ	, ret+16(FP)
 	RET
 
 TEXT runtime·casuintptr(SB), NOSPLIT, $0-17
@@ -434,13 +429,7 @@ TEXT runtime·cas64(SB), NOSPLIT, $0-25
 	MOVQ	new+16(FP), CX
 	LOCK
 	CMPXCHGQ	CX, 0(BX)
-	JNZ	fail
-	MOVL	$1, AX
-	MOVB	AX, ret+24(FP)
-	RET
-fail:
-	MOVL	$0, AX
-	MOVB	AX, ret+24(FP)
+	SETEQ	, ret+24(FP)
 	RET
 
 // bool casp(void **val, void *old, void *new)
@@ -456,12 +445,7 @@ TEXT runtime·casp1(SB), NOSPLIT, $0-17
 	MOVL	new+8(FP), CX
 	LOCK
 	CMPXCHGL	CX, 0(BX)
-	JZ 4(PC)
-	MOVL	$0, AX
-	MOVB	AX, ret+16(FP)
-	RET
-	MOVL	$1, AX
-	MOVB	AX, ret+16(FP)
+	SETEQ	, ret+16(FP)
 	RET
 
 // uint32 xadd(uint32 volatile *val, int32 delta)