diff --git a/src/cmd/compile/internal/ssa/gen/AMD64.rules b/src/cmd/compile/internal/ssa/gen/AMD64.rules
index ee9ccfb41c..f7eb92dc8b 100644
--- a/src/cmd/compile/internal/ssa/gen/AMD64.rules
+++ b/src/cmd/compile/internal/ssa/gen/AMD64.rules
@@ -1429,11 +1429,11 @@
 (NOTQ (MOVQconst [c])) -> (MOVQconst [^c])
 (NOTL (MOVLconst [c])) -> (MOVLconst [^c])
 (BTSQconst [c] (MOVQconst [d])) -> (MOVQconst [d|(1<<uint32(c))])
-(BTSLconst [c] (MOVLconst [d])) -> (MOVLconst [d|(1<<uint32(c))])
+(BTSLconst [c] (MOVLconst [d])) => (MOVLconst [d|(1<<uint32(c))])
 (BTRQconst [c] (MOVQconst [d])) -> (MOVQconst [d&^(1<<uint32(c))])
-(BTRLconst [c] (MOVLconst [d])) -> (MOVLconst [d&^(1<<uint32(c))])
+(BTRLconst [c] (MOVLconst [d])) => (MOVLconst [d&^(1<<uint32(c))])
 (BTCQconst [c] (MOVQconst [d])) -> (MOVQconst [d^(1<<uint32(c))])
-(BTCLconst [c] (MOVLconst [d])) -> (MOVLconst [d^(1<<uint32(c))])
+(BTCLconst [c] (MOVLconst [d])) => (MOVLconst [d^(1<<uint32(c))])
 
 // If c or d doesn't fit into 32 bits, then we can't construct ORQconst,
 // but we can still constant-fold.
diff --git a/src/cmd/compile/internal/ssa/rewriteAMD64.go b/src/cmd/compile/internal/ssa/rewriteAMD64.go
index 72ed1eb62c..e59fa208c1 100644
--- a/src/cmd/compile/internal/ssa/rewriteAMD64.go
+++ b/src/cmd/compile/internal/ssa/rewriteAMD64.go
@@ -3526,13 +3526,13 @@ func rewriteValueAMD64_OpAMD64BTCLconst(v *Value) bool {
 	// match: (BTCLconst [c] (MOVLconst [d]))
 	// result: (MOVLconst [d^(1<<uint32(c))])
 	for {
-		c := v.AuxInt
+		c := auxIntToInt8(v.AuxInt)
 		if v_0.Op != OpAMD64MOVLconst {
 			break
 		}
-		d := v_0.AuxInt
+		d := auxIntToInt32(v_0.AuxInt)
 		v.reset(OpAMD64MOVLconst)
-		v.AuxInt = d ^ (1 << uint32(c))
+		v.AuxInt = int32ToAuxInt(d ^ (1 << uint32(c)))
 		return true
 	}
 	return false
@@ -4010,13 +4010,13 @@ func rewriteValueAMD64_OpAMD64BTRLconst(v *Value) bool {
 	// match: (BTRLconst [c] (MOVLconst [d]))
 	// result: (MOVLconst [d&^(1<<uint32(c))])
 	for {
-		c := v.AuxInt
+		c := auxIntToInt8(v.AuxInt)
 		if v_0.Op != OpAMD64MOVLconst {
 			break
 		}
-		d := v_0.AuxInt
+		d := auxIntToInt32(v_0.AuxInt)
 		v.reset(OpAMD64MOVLconst)
-		v.AuxInt = d &^ (1 << uint32(c))
+		v.AuxInt = int32ToAuxInt(d &^ (1 << uint32(c)))
 		return true
 	}
 	return false
@@ -4356,13 +4356,13 @@ func rewriteValueAMD64_OpAMD64BTSLconst(v *Value) bool {
 	// match: (BTSLconst [c] (MOVLconst [d]))
 	// result: (MOVLconst [d|(1<<uint32(c))])
 	for {
-		c := v.AuxInt
+		c := auxIntToInt8(v.AuxInt)
 		if v_0.Op != OpAMD64MOVLconst {
 			break
 		}
-		d := v_0.AuxInt
+		d := auxIntToInt32(v_0.AuxInt)
 		v.reset(OpAMD64MOVLconst)
-		v.AuxInt = d | (1 << uint32(c))
+		v.AuxInt = int32ToAuxInt(d | (1 << uint32(c)))
 		return true
 	}
 	return false
diff --git a/test/fixedbugs/issue42753.go b/test/fixedbugs/issue42753.go
new file mode 100644
index 0000000000..a998d1d3b3
--- /dev/null
+++ b/test/fixedbugs/issue42753.go
@@ -0,0 +1,13 @@
+// compile -d=ssa/check/on
+
+// Copyright 2020 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 main
+
+func f() uint32 {
+	s := "\x01"
+	x := -int32(s[0])
+	return uint32(x) & 0x7fffffff
+}