diff --git a/src/net/http/triv.go b/src/net/http/triv.go
index 4c2160bbc3..1e2eea22b7 100644
--- a/src/net/http/triv.go
+++ b/src/net/http/triv.go
@@ -50,7 +50,7 @@ func (ctr *Counter) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 		ctr.n++
 	case "POST":
 		var buf strings.Builder
-		io.Copy(buf, req.Body)
+		io.Copy(&buf, req.Body)
 		body := buf.String()
 		if n, err := strconv.Atoi(body); err != nil {
 			fmt.Fprintf(w, "bad POST: %v\nbody: [%v]\n", err, body)