diff --git a/src/cmd/compile/internal/amd64/ssa.go b/src/cmd/compile/internal/amd64/ssa.go
index 49ef415e66..d5e9fd32f0 100644
--- a/src/cmd/compile/internal/amd64/ssa.go
+++ b/src/cmd/compile/internal/amd64/ssa.go
@@ -266,7 +266,15 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 
 		// Issue -1 fixup code.
 		// n / -1 = -n
-		n1 := s.Prog(x86.ANEGQ)
+		var n1 *obj.Prog
+		switch v.Op {
+		case ssa.OpAMD64DIVQ:
+			n1 = s.Prog(x86.ANEGQ)
+		case ssa.OpAMD64DIVL:
+			n1 = s.Prog(x86.ANEGL)
+		case ssa.OpAMD64DIVW:
+			n1 = s.Prog(x86.ANEGW)
+		}
 		n1.To.Type = obj.TYPE_REG
 		n1.To.Reg = x86.REG_AX
 
diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index df5f6c9fa4..587a2a6d1a 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -782,12 +782,8 @@ func zeroUpper32Bits(x *Value, depth int) bool {
 		OpAMD64ANDL, OpAMD64ANDLconst, OpAMD64ORL, OpAMD64ORLconst,
 		OpAMD64XORL, OpAMD64XORLconst, OpAMD64NEGL, OpAMD64NOTL:
 		return true
-	case OpArg:
+	case OpArg, OpSelect0, OpSelect1:
 		return x.Type.Width == 4
-	case OpSelect0, OpSelect1:
-		// Disabled for now. See issue 23305.
-		// TODO: we could look into the arg of the Select to decide.
-		return false
 	case OpPhi:
 		// Phis can use each-other as an arguments, instead of tracking visited values,
 		// just limit recursion depth.
diff --git a/src/cmd/compile/internal/ssa/zeroextension_test.go b/src/cmd/compile/internal/ssa/zeroextension_test.go
new file mode 100644
index 0000000000..692685eaa4
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/zeroextension_test.go
@@ -0,0 +1,34 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ssa
+
+import "testing"
+
+type extTest struct {
+	f    func(uint64, uint64) uint64
+	arg1 uint64
+	arg2 uint64
+	res  uint64
+	name string
+}
+
+var extTests = [...]extTest{
+	{f: func(a, b uint64) uint64 { op1 := int32(a); op2 := int32(b); return uint64(uint32(op1 / op2)) }, arg1: 0x1, arg2: 0xfffffffeffffffff, res: 0xffffffff, name: "div"},
+	{f: func(a, b uint64) uint64 { op1 := int32(a); op2 := int32(b); return uint64(uint32(op1 * op2)) }, arg1: 0x1, arg2: 0x100000001, res: 0x1, name: "mul"},
+	{f: func(a, b uint64) uint64 { op1 := int32(a); op2 := int32(b); return uint64(uint32(op1 + op2)) }, arg1: 0x1, arg2: 0xfffffffffffffff, res: 0x0, name: "add"},
+	{f: func(a, b uint64) uint64 { op1 := int32(a); op2 := int32(b); return uint64(uint32(op1 - op2)) }, arg1: 0x1, arg2: 0xfffffffffffffff, res: 0x2, name: "sub"},
+	{f: func(a, b uint64) uint64 { op1 := int32(a); op2 := int32(b); return uint64(uint32(op1 | op2)) }, arg1: 0x1, arg2: 0xfffffffffffffff, res: 0xffffffff, name: "or"},
+	{f: func(a, b uint64) uint64 { op1 := int32(a); op2 := int32(b); return uint64(uint32(op1 ^ op2)) }, arg1: 0x1, arg2: 0xfffffffffffffff, res: 0xfffffffe, name: "xor"},
+	{f: func(a, b uint64) uint64 { op1 := int32(a); op2 := int32(b); return uint64(uint32(op1 & op2)) }, arg1: 0x1, arg2: 0x100000000000001, res: 0x1, name: "and"},
+}
+
+func TestZeroExtension(t *testing.T) {
+	for _, x := range extTests {
+		r := x.f(x.arg1, x.arg2)
+		if x.res != r {
+			t.Errorf("%s: got %d want %d", x.name, r, x.res)
+		}
+	}
+}