diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index b8a9062d830..bdc4f799aa2 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -1492,7 +1492,7 @@ func mergePPC64AndSrwi(m, s int64) int64 {
 	if !isPPC64WordRotateMask(mask) {
 		return 0
 	}
-	return encodePPC64RotateMask(32-s, mask, 32)
+	return encodePPC64RotateMask((32-s)&31, mask, 32)
 }
 
 // Test if a shift right feeding into a CLRLSLDI can be merged into RLWINM.
diff --git a/src/cmd/compile/internal/ssa/rewrite_test.go b/src/cmd/compile/internal/ssa/rewrite_test.go
index 272b080d881..357fe1183fa 100644
--- a/src/cmd/compile/internal/ssa/rewrite_test.go
+++ b/src/cmd/compile/internal/ssa/rewrite_test.go
@@ -205,6 +205,7 @@ func TestMergePPC64AndSrwi(t *testing.T) {
 		{0x00000000, 4, false, 0, 0},
 		{0xF0000000, 4, false, 0, 0},
 		{0xF0000000, 32, false, 0, 0},
+		{0xFFFFFFFF, 0, true, 0, 0xFFFFFFFF},
 	}
 	for i, v := range tests {
 		result := mergePPC64AndSrwi(v.and, v.srw)