diff --git a/src/cmd/compile/internal/walk/switch.go b/src/cmd/compile/internal/walk/switch.go
index b03bc3eba7..59446ef3db 100644
--- a/src/cmd/compile/internal/walk/switch.go
+++ b/src/cmd/compile/internal/walk/switch.go
@@ -201,10 +201,15 @@ func (s *exprSwitch) flush() {
 
 	// Merge consecutive integer cases.
 	if s.exprname.Type().IsInteger() {
+		consecutive := func(last, next constant.Value) bool {
+			delta := constant.BinaryOp(next, token.SUB, last)
+			return constant.Compare(delta, token.EQL, constant.MakeInt64(1))
+		}
+
 		merged := cc[:1]
 		for _, c := range cc[1:] {
 			last := &merged[len(merged)-1]
-			if last.jmp == c.jmp && ir.Int64Val(last.hi)+1 == ir.Int64Val(c.lo) {
+			if last.jmp == c.jmp && consecutive(last.hi.Val(), c.lo.Val()) {
 				last.hi = c.lo
 			} else {
 				merged = append(merged, c)
diff --git a/test/fixedbugs/issue43480.go b/test/fixedbugs/issue43480.go
new file mode 100644
index 0000000000..d98ad3a34e
--- /dev/null
+++ b/test/fixedbugs/issue43480.go
@@ -0,0 +1,33 @@
+// run
+
+// 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.
+
+// Issue #43480: ICE on large uint64 constants in switch cases.
+
+package main
+
+func isPow10(x uint64) bool {
+	switch x {
+	case 1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
+		1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19:
+		return true
+	}
+	return false
+}
+
+func main() {
+	var x uint64 = 1
+
+	for {
+		if !isPow10(x) || isPow10(x-1) || isPow10(x+1) {
+			panic(x)
+		}
+		next := x * 10
+		if next/10 != x {
+			break // overflow
+		}
+		x = next
+	}
+}