diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index 39aa63d..24efd38 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -1427,10 +1427,11 @@
 	return
 }
 
-// This verifies that the mask occupies the
-// rightmost bits.
+// This verifies that the mask is a set of
+// consecutive bits including the least
+// significant bit.
 func isPPC64ValidShiftMask(v int64) bool {
-	if ((v + 1) & v) == 0 {
+	if (v != 0) && ((v+1)&v) == 0 {
 		return true
 	}
 	return false
diff --git a/test/codegen/issue42610.go b/test/codegen/issue42610.go
new file mode 100644
index 0000000..c7eeddc
--- /dev/null
+++ b/test/codegen/issue42610.go
@@ -0,0 +1,30 @@
+// asmcheck
+
+// 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.
+
+// Don't allow 0 masks in shift lowering rules on ppc64x.
+// See issue 42610.
+
+package codegen
+
+func f32(a []int32, i uint32) {
+        g := func(p int32) int32 {
+                i = uint32(p) * (uint32(p) & (i & 1))
+                return 1
+        }
+        // ppc64le: -"RLWNIM"
+        // ppc64: -"RLWNIM"
+        a[0] = g(8) >> 1
+}
+
+func f(a []int, i uint) {
+	g := func(p int) int {
+		i = uint(p) * (uint(p) & (i & 1))
+		return 1
+	}
+	// ppc64le: -"RLDIC"
+	// ppc64: -"RLDIC"
+	a[0] = g(8) >> 1
+}