diff --git a/src/cmd/asm/internal/asm/testdata/arm64.s b/src/cmd/asm/internal/asm/testdata/arm64.s
index c0e2fb7e0e..69267bfa63 100644
--- a/src/cmd/asm/internal/asm/testdata/arm64.s
+++ b/src/cmd/asm/internal/asm/testdata/arm64.s
@@ -274,6 +274,9 @@ TEXT	foo(SB), DUPOK|NOSPLIT, $-8
 	ADDW	$0x60060, R2                        // ADDW	$393312, R2                     // 4280011142804111
 	CMPW	$0x60060, R2                        // CMPW	$393312, R2                     // 1b0c8052db00a0725f001b6b
 
+	// TODO: this could have better encoding
+	ANDW	$-1, R10 // 1b0080124a011b0a
+
 	AND	$8, R0, RSP // 1f007d92
 	ORR	$8, R0, RSP // 1f007db2
 	EOR	$8, R0, RSP // 1f007dd2
diff --git a/src/cmd/internal/obj/arm64/asm7.go b/src/cmd/internal/obj/arm64/asm7.go
index 9a1908a655..7f5cba645a 100644
--- a/src/cmd/internal/obj/arm64/asm7.go
+++ b/src/cmd/internal/obj/arm64/asm7.go
@@ -1639,12 +1639,12 @@ func (c *ctxt7) con32class(a *obj.Addr) int {
 	}
 	if isaddcon(int64(v)) {
 		if v <= 0xFFF {
-			if isbitcon(uint64(v)) {
+			if isbitcon(uint64(a.Offset)) {
 				return C_ABCON0
 			}
 			return C_ADDCON0
 		}
-		if isbitcon(uint64(v)) {
+		if isbitcon(uint64(a.Offset)) {
 			return C_ABCON
 		}
 		if movcon(int64(v)) >= 0 {
@@ -1658,7 +1658,7 @@ func (c *ctxt7) con32class(a *obj.Addr) int {
 
 	t := movcon(int64(v))
 	if t >= 0 {
-		if isbitcon(uint64(v)) {
+		if isbitcon(uint64(a.Offset)) {
 			return C_MBCON
 		}
 		return C_MOVCON
@@ -1666,13 +1666,13 @@ func (c *ctxt7) con32class(a *obj.Addr) int {
 
 	t = movcon(int64(^v))
 	if t >= 0 {
-		if isbitcon(uint64(v)) {
+		if isbitcon(uint64(a.Offset)) {
 			return C_MBCON
 		}
 		return C_MOVCON
 	}
 
-	if isbitcon(uint64(v)) {
+	if isbitcon(uint64(a.Offset)) {
 		return C_BITCON
 	}