diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index b32823283b..eb2c3b31b8 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -1583,6 +1583,11 @@ func GetPPC64Shiftme(auxint int64) int64 {
 // operation.  Masks can also extend from the msb and wrap to
 // the lsb too.  That is, the valid masks are 32 bit strings
 // of the form: 0..01..10..0 or 1..10..01..1 or 1...1
+//
+// Note: This ignores the upper 32 bits of the input. When a
+// zero extended result is desired (e.g a 64 bit result), the
+// user must verify the upper 32 bits are 0 and the mask is
+// contiguous (that is, non-wrapping).
 func isPPC64WordRotateMask(v64 int64) bool {
 	// Isolate rightmost 1 (if none 0) and add.
 	v := uint32(v64)
@@ -1593,6 +1598,16 @@ func isPPC64WordRotateMask(v64 int64) bool {
 	return (v&vp == 0 || vn&vpn == 0) && v != 0
 }
 
+// Test if this mask is a valid, contiguous bitmask which can be
+// represented by a RLWNM mask and also clears the upper 32 bits
+// of the register.
+func isPPC64WordRotateMaskNonWrapping(v64 int64) bool {
+	// Isolate rightmost 1 (if none 0) and add.
+	v := uint32(v64)
+	vp := (v & -v) + v
+	return (v&vp == 0) && v != 0 && uint64(uint32(v64)) == uint64(v64)
+}
+
 // Compress mask and shift into single value of the form
 // me | mb<<8 | rotate<<16 | nbits<<24 where me and mb can
 // be used to regenerate the input mask.
@@ -1702,7 +1717,7 @@ func mergePPC64AndSrdi(m, s int64) int64 {
 	if rv&uint64(mask) != 0 {
 		return 0
 	}
-	if !isPPC64WordRotateMask(mask) {
+	if !isPPC64WordRotateMaskNonWrapping(mask) {
 		return 0
 	}
 	return encodePPC64RotateMask((32-s)&31, mask, 32)
@@ -1717,7 +1732,7 @@ func mergePPC64AndSldi(m, s int64) int64 {
 	if rv&uint64(mask) != 0 {
 		return 0
 	}
-	if !isPPC64WordRotateMask(mask) {
+	if !isPPC64WordRotateMaskNonWrapping(mask) {
 		return 0
 	}
 	return encodePPC64RotateMask(s&31, mask, 32)
diff --git a/test/codegen/shift.go b/test/codegen/shift.go
index 56e8d354e6..0e4cf1ed8d 100644
--- a/test/codegen/shift.go
+++ b/test/codegen/shift.go
@@ -529,6 +529,16 @@ func checkMergedShifts64(a [256]uint32, b [256]uint64, c [256]byte, v uint64) {
 	b[1] = b[(v>>20)&0xFF]
 	// ppc64x: "RLWNM", -"SLD"
 	b[2] = b[((uint64((uint32(v) >> 21)) & 0x3f) << 4)]
+	// ppc64x: -"RLWNM"
+	b[3] = (b[3] << 24) & 0xFFFFFF000000
+	// ppc64x: "RLWNM\t[$]24, R[0-9]+, [$]0, [$]7,"
+	b[4] = (b[4] << 24) & 0xFF000000
+	// ppc64x: "RLWNM\t[$]24, R[0-9]+, [$]0, [$]7,"
+	b[5] = (b[5] << 24) & 0xFF00000F
+	// ppc64x: -"RLWNM"
+	b[6] = (b[6] << 0) & 0xFF00000F
+	// ppc64x: "RLWNM\t[$]4, R[0-9]+, [$]28, [$]31,"
+	b[7] = (b[7] >> 28) & 0xF
 	// ppc64x: "RLWNM\t[$]11, R[0-9]+, [$]10, [$]15"
 	c[0] = c[((v>>5)&0x3F)<<16]
 	// ppc64x: "ANDCC\t[$]8064,"