diff --git a/server/handlers.go b/server/handlers.go
index babd5417..f7330440 100644
--- a/server/handlers.go
+++ b/server/handlers.go
@@ -283,7 +283,7 @@ func (s *Server) handleConnectorLogin(w http.ResponseWriter, r *http.Request) {
 	connID := mux.Vars(r)["connector"]
 	conn, err := s.getConnector(connID)
 	if err != nil {
-		s.logger.Errorf("Failed to create authorization request: %v", err)
+		s.logger.Errorf("Failed to get connector: %v", err)
 		s.renderError(r, w, http.StatusBadRequest, "Requested resource does not exist")
 		return
 	}
@@ -304,6 +304,9 @@ func (s *Server) handleConnectorLogin(w http.ResponseWriter, r *http.Request) {
 	// Set the connector being used for the login.
 	if authReq.ConnectorID != connID {
 		updater := func(a storage.AuthRequest) (storage.AuthRequest, error) {
+			if a.ConnectorID != "" {
+				return a, fmt.Errorf("connector is already set for this auth request")
+			}
 			a.ConnectorID = connID
 			return a, nil
 		}
diff --git a/server/handlers_test.go b/server/handlers_test.go
index b30076dd..12dce3a8 100644
--- a/server/handlers_test.go
+++ b/server/handlers_test.go
@@ -8,8 +8,12 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"testing"
+	"time"
+
+	"github.com/gorilla/mux"
 
 	"github.com/dexidp/dex/storage"
+	"github.com/dexidp/dex/storage/memory"
 )
 
 func TestHandleHealth(t *testing.T) {
@@ -119,3 +123,84 @@ func TestHandleInvalidSAMLCallbacks(t *testing.T) {
 		}
 	}
 }
+
+func TestConnectorLoginDoesNotAllowToChangeConnectorForAuthRequest(t *testing.T) {
+	memStorage := memory.New(logger)
+
+	templates, err := loadTemplates(webConfig{}, "../web/templates")
+	if err != nil {
+		t.Fatal("failed to load tempalates")
+	}
+
+	s := &Server{
+		storage:                memStorage,
+		logger:                 logger,
+		templates:              templates,
+		supportedResponseTypes: map[string]bool{"code": true},
+		now:                    time.Now,
+		connectors:             make(map[string]Connector),
+	}
+
+	r := mux.NewRouter()
+	r.HandleFunc("/auth/{connector}", s.handleConnectorLogin)
+	s.mux = r
+
+	clientID := "clientID"
+	clientSecret := "secret"
+	redirectURL := "localhost:5555" + "/callback"
+	client := storage.Client{
+		ID:           clientID,
+		Secret:       clientSecret,
+		RedirectURIs: []string{redirectURL},
+	}
+	if err := memStorage.CreateClient(client); err != nil {
+		t.Fatal("failed to create client")
+	}
+
+	createConnector := func(t *testing.T, id string) storage.Connector {
+		connector := storage.Connector{
+			ID:              id,
+			Type:            "mockCallback",
+			Name:            "Mock",
+			ResourceVersion: "1",
+		}
+		if err := memStorage.CreateConnector(connector); err != nil {
+			t.Fatalf("failed to create connector %v", id)
+		}
+
+		return connector
+	}
+
+	connector1 := createConnector(t, "mock1")
+	connector2 := createConnector(t, "mock2")
+
+	authReq := storage.AuthRequest{
+		ID: storage.NewID(),
+	}
+	if err := memStorage.CreateAuthRequest(authReq); err != nil {
+		t.Fatal("failed to create auth request")
+	}
+
+	createConnectorLoginRequest := func(connID string) *http.Request {
+		req := httptest.NewRequest("GET", "/auth/"+connID, nil)
+		q := req.URL.Query()
+		q.Add("req", authReq.ID)
+		q.Add("redirect_uri", redirectURL)
+		q.Add("scope", "openid")
+		q.Add("response_type", "code")
+		req.URL.RawQuery = q.Encode()
+		return req
+	}
+
+	recorder := httptest.NewRecorder()
+	s.ServeHTTP(recorder, createConnectorLoginRequest(connector1.ID))
+	if recorder.Code != 302 {
+		t.Fatal("failed to process request")
+	}
+
+	recorder2 := httptest.NewRecorder()
+	s.ServeHTTP(recorder2, createConnectorLoginRequest(connector2.ID))
+	if recorder2.Code != 500 {
+		t.Error("attempt to overwrite connector on auth request should fail")
+	}
+}