diff --git a/mackerel-plugin-elasticsearch/lib/elasticsearch_test.go b/mackerel-plugin-elasticsearch/lib/elasticsearch_test.go
index 903dd755e..747b1ca4c 100644
--- a/mackerel-plugin-elasticsearch/lib/elasticsearch_test.go
+++ b/mackerel-plugin-elasticsearch/lib/elasticsearch_test.go
@@ -16,7 +16,7 @@ var testHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request)
 		panic(err)
 	}
 
-	fmt.Fprintf(w, string(json))
+	fmt.Fprint(w, string(json))
 })
 
 func TestGraphDefinition(t *testing.T) {
diff --git a/mackerel-plugin-solr/lib/solr_test.go b/mackerel-plugin-solr/lib/solr_test.go
index 3b29ac4bc..faafa7bdd 100644
--- a/mackerel-plugin-solr/lib/solr_test.go
+++ b/mackerel-plugin-solr/lib/solr_test.go
@@ -18,14 +18,14 @@ var (
 var testHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 	switch r.URL.Path {
 	case "/solr/admin/info/system":
-		fmt.Fprintf(w, fetchJSON("system"))
+		fmt.Fprint(w, fetchJSON("system"))
 	case "/solr/admin/cores":
-		fmt.Fprintf(w, fetchJSON("cores"))
+		fmt.Fprint(w, fetchJSON("cores"))
 	case "/solr/testcore/admin/mbeans":
 		key := r.URL.Query()["cat"][0]
-		fmt.Fprintf(w, fetchJSONForMbeans(key))
+		fmt.Fprint(w, fetchJSONForMbeans(key))
 	default:
-		fmt.Fprintf(w, "")
+		fmt.Fprint(w, "")
 	}
 })