diff --git a/src/cmd/compile/internal/ssa/redblack32_test.go b/src/cmd/compile/internal/ssa/redblack32_test.go
index 1ec2976072..376e8cff8d 100644
--- a/src/cmd/compile/internal/ssa/redblack32_test.go
+++ b/src/cmd/compile/internal/ssa/redblack32_test.go
@@ -134,15 +134,15 @@ func (t *RBTint32) DebugString() string {
 func (t *node32) DebugString() string {
 	s := ""
 	if t.left != nil {
-		s = s + "["
-		s = s + t.left.DebugString()
-		s = s + "]"
+		s += "["
+		s += t.left.DebugString()
+		s += "]"
 	}
-	s = s + fmt.Sprintf("%v=%v:%d", t.key, t.data, t.rank)
+	s += fmt.Sprintf("%v=%v:%d", t.key, t.data, t.rank)
 	if t.right != nil {
-		s = s + "["
-		s = s + t.right.DebugString()
-		s = s + "]"
+		s += "["
+		s += t.right.DebugString()
+		s += "]"
 	}
 	return s
 }