diff --git a/helper/communicator/config.go b/helper/communicator/config.go
index 0f19c4e68..53de3f81e 100644
--- a/helper/communicator/config.go
+++ b/helper/communicator/config.go
@@ -65,6 +65,10 @@ func (c *Config) Prepare(ctx *interpolate.Context) []error {
 		if es := c.prepareWinRM(ctx); len(es) > 0 {
 			errs = append(errs, es...)
 		}
+	case "none":
+		break
+	default:
+		return []error{fmt.Errorf("Communicator type %s is invalid", c.Type)}
 	}
 
 	return errs
diff --git a/helper/communicator/config_test.go b/helper/communicator/config_test.go
index dc1bd965d..cbdaafa98 100644
--- a/helper/communicator/config_test.go
+++ b/helper/communicator/config_test.go
@@ -30,6 +30,23 @@ func TestConfig_none(t *testing.T) {
 	}
 }
 
+func TestConfig_badtype(t *testing.T) {
+	c := &Config{Type: "foo"}
+	if err := c.Prepare(testContext(t)); len(err) != 1 {
+		t.Fatalf("bad: %#v", err)
+	}
+}
+
+func TestConfig_winrm(t *testing.T) {
+	c := &Config{
+		Type:      "winrm",
+		WinRMUser: "admin",
+	}
+	if err := c.Prepare(testContext(t)); len(err) > 0 {
+		t.Fatalf("bad: %#v", err)
+	}
+}
+
 func testContext(t *testing.T) *interpolate.Context {
 	return nil
 }