diff --git a/vendor/cmd/go/internal/modfetch/cache.go b/vendor/cmd/go/internal/modfetch/cache.go
index cc7a34b..b7cf4a5 100644
--- a/vendor/cmd/go/internal/modfetch/cache.go
+++ b/vendor/cmd/go/internal/modfetch/cache.go
@@ -324,7 +324,7 @@
 		return err
 	}
 	// Write data to temp file next to target file.
-	f, err := ioutil.TempFile(filepath.Dir(file), filepath.Base(file)+".tmp*")
+	f, err := ioutil.TempFile(filepath.Dir(file), filepath.Base(file)+".tmp-")
 	if err != nil {
 		return err
 	}
diff --git a/vendor/cmd/go/internal/modfetch/cache_test.go b/vendor/cmd/go/internal/modfetch/cache_test.go
new file mode 100644
index 0000000..87b1cdc
--- /dev/null
+++ b/vendor/cmd/go/internal/modfetch/cache_test.go
@@ -0,0 +1,25 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package modfetch
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestWriteDiskCache(t *testing.T) {
+	tmpdir, err := ioutil.TempDir("", "vgo-writeCache-test-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpdir)
+
+	err = writeDiskCache(filepath.Join(tmpdir, "file"), []byte("data"))
+	if err != nil {
+		t.Fatal(err)
+	}
+}