diff --git a/clientconn.go b/clientconn.go
index 52d47a57..fc13c38d 100644
--- a/clientconn.go
+++ b/clientconn.go
@@ -50,6 +50,10 @@ import (
 var (
 	// ErrUnspecTarget indicates that the target address is unspecified.
 	ErrUnspecTarget = errors.New("grpc: target is unspecified")
+	// ErrNoTransportSecurity indicates that there is no transport security
+	// being set for ClientConn. Users should either set one or explicityly
+	// call WithInsecure DialOption to disable security.
+	ErrNoTransportSecurity = errors.New("grpc: no transport security set")
 	// ErrClientConnClosing indicates that the operation is illegal because
 	// the session is closing.
 	ErrClientConnClosing = errors.New("grpc: the client connection is closing")
@@ -63,9 +67,10 @@ var (
 // dialOptions configure a Dial call. dialOptions are set by the DialOption
 // values passed to Dial.
 type dialOptions struct {
-	codec Codec
-	block bool
-	copts transport.ConnectOptions
+	codec    Codec
+	block    bool
+	insecure bool
+	copts    transport.ConnectOptions
 }
 
 // DialOption configures how we set up the connection.
@@ -87,6 +92,12 @@ func WithBlock() DialOption {
 	}
 }
 
+func WithInsecure() DialOption {
+	return func(o *dialOptions) {
+		o.insecure = true
+	}
+}
+
 // WithTransportCredentials returns a DialOption which configures a
 // connection level security credentials (e.g., TLS/SSL).
 func WithTransportCredentials(creds credentials.TransportAuthenticator) DialOption {
@@ -136,6 +147,18 @@ func Dial(target string, opts ...DialOption) (*ClientConn, error) {
 	for _, opt := range opts {
 		opt(&cc.dopts)
 	}
+	if !cc.dopts.insecure {
+		var ok bool
+		for _, c := range cc.dopts.copts.AuthOptions {
+			if _, ok := c.(credentials.TransportAuthenticator); !ok {
+				continue
+			}
+			ok = true
+		}
+		if !ok {
+			return nil, ErrNoTransportSecurity
+		}
+	}
 	colonPos := strings.LastIndex(target, ":")
 	if colonPos == -1 {
 		colonPos = len(target)
diff --git a/test/end2end_test.go b/test/end2end_test.go
index 35b40ec0..a14770c3 100644
--- a/test/end2end_test.go
+++ b/test/end2end_test.go
@@ -237,7 +237,7 @@ func (s *testServer) HalfDuplexCall(stream testpb.TestService_HalfDuplexCallServ
 const tlsDir = "testdata/"
 
 func TestDialTimeout(t *testing.T) {
-	conn, err := grpc.Dial("Non-Existent.Server:80", grpc.WithTimeout(time.Millisecond), grpc.WithBlock())
+	conn, err := grpc.Dial("Non-Existent.Server:80", grpc.WithTimeout(time.Millisecond), grpc.WithBlock(), grpc.WithInsecure())
 	if err == nil {
 		conn.Close()
 	}
@@ -251,7 +251,7 @@ func TestTLSDialTimeout(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Failed to create credentials %v", err)
 	}
-	conn, err := grpc.Dial("Non-Existent.Server:80", grpc.WithTransportCredentials(creds), grpc.WithTimeout(time.Millisecond), grpc.WithBlock())
+	conn, err := grpc.Dial("Non-Existent.Server:80", grpc.WithTransportCredentials(creds), grpc.WithTimeout(time.Millisecond), grpc.WithBlock(), grpc.WithInsecure())
 	if err == nil {
 		conn.Close()
 	}
@@ -270,7 +270,7 @@ func TestReconnectTimeout(t *testing.T) {
 		t.Fatalf("Failed to parse listener address: %v", err)
 	}
 	addr := "localhost:" + port
-	conn, err := grpc.Dial(addr, grpc.WithTimeout(5*time.Second), grpc.WithBlock())
+	conn, err := grpc.Dial(addr, grpc.WithTimeout(5*time.Second), grpc.WithBlock(), grpc.WithInsecure())
 	if err != nil {
 		t.Fatalf("Failed to dial to the server %q: %v", addr, err)
 	}
@@ -357,7 +357,7 @@ func setUp(hs *health.HealthServer, maxStream uint32, ua string, e env) (s *grpc
 		}
 		cc, err = grpc.Dial(addr, grpc.WithTransportCredentials(creds), grpc.WithDialer(e.dialer), grpc.WithUserAgent(ua))
 	} else {
-		cc, err = grpc.Dial(addr, grpc.WithDialer(e.dialer), grpc.WithUserAgent(ua))
+		cc, err = grpc.Dial(addr, grpc.WithDialer(e.dialer), grpc.WithInsecure(), grpc.WithUserAgent(ua))
 	}
 	if err != nil {
 		grpclog.Fatalf("Dial(%q) = %v", addr, err)