diff --git a/pkg/services/authn/authnimpl/sync/user_sync.go b/pkg/services/authn/authnimpl/sync/user_sync.go
index d72b391222b..6796c7c723f 100644
--- a/pkg/services/authn/authnimpl/sync/user_sync.go
+++ b/pkg/services/authn/authnimpl/sync/user_sync.go
@@ -136,9 +136,13 @@ func (s *UserSync) SyncLastSeenHook(ctx context.Context, identity *authn.Identit
 
 	namespace, id := identity.NamespacedID()
 
+	// do not sync invalid users
+	if id <= 0 {
+		return nil // skip sync
+	}
+
 	if namespace != authn.NamespaceUser && namespace != authn.NamespaceServiceAccount {
-		// skip sync
-		return nil
+		return nil // skip sync
 	}
 
 	go func(userID int64) {
diff --git a/pkg/services/user/model.go b/pkg/services/user/model.go
index d30ad324980..588933a9c09 100644
--- a/pkg/services/user/model.go
+++ b/pkg/services/user/model.go
@@ -26,6 +26,7 @@ var (
 	ErrProtectedUser     = errors.New("cannot adopt protected user")
 	ErrNoUniqueID        = errors.New("identifying id not found")
 	ErrLastSeenUpToDate  = errors.New("last seen is already up to date")
+	ErrUpdateInvalidID   = errors.New("unable to update invalid id")
 )
 
 type User struct {
diff --git a/pkg/services/user/userimpl/store.go b/pkg/services/user/userimpl/store.go
index 51e99a91372..54680dc6a9a 100644
--- a/pkg/services/user/userimpl/store.go
+++ b/pkg/services/user/userimpl/store.go
@@ -368,6 +368,9 @@ func (ss *sqlStore) ChangePassword(ctx context.Context, cmd *user.ChangeUserPass
 }
 
 func (ss *sqlStore) UpdateLastSeenAt(ctx context.Context, cmd *user.UpdateUserLastSeenAtCommand) error {
+	if cmd.UserID <= 0 {
+		return user.ErrUpdateInvalidID
+	}
 	return ss.db.WithTransactionalDbSession(ctx, func(sess *db.Session) error {
 		user := user.User{
 			ID:         cmd.UserID,
@@ -421,6 +424,8 @@ func (ss *sqlStore) GetSignedInUser(ctx context.Context, query *user.GetSignedIn
 			} else {
 				sess.SQL(rawSQL+"WHERE u.email=?", query.Email)
 			}
+		default:
+			return user.ErrNoUniqueID
 		}
 		has, err := sess.Get(&signedInUser)
 		if err != nil {
diff --git a/pkg/services/user/userimpl/store_test.go b/pkg/services/user/userimpl/store_test.go
index e617478d161..1291d1d4cbc 100644
--- a/pkg/services/user/userimpl/store_test.go
+++ b/pkg/services/user/userimpl/store_test.go
@@ -349,8 +349,15 @@ func TestIntegrationUserDataAccess(t *testing.T) {
 	})
 
 	t.Run("update last seen at", func(t *testing.T) {
-		err := userStore.UpdateLastSeenAt(context.Background(), &user.UpdateUserLastSeenAtCommand{})
+		err := userStore.UpdateLastSeenAt(context.Background(), &user.UpdateUserLastSeenAtCommand{
+			UserID: 10, // Requires UserID
+		})
 		require.NoError(t, err)
+
+		err = userStore.UpdateLastSeenAt(context.Background(), &user.UpdateUserLastSeenAtCommand{
+			UserID: -1,
+		})
+		require.Error(t, err)
 	})
 
 	t.Run("get signed in user", func(t *testing.T) {
@@ -382,6 +389,15 @@ func TestIntegrationUserDataAccess(t *testing.T) {
 		result, err := userStore.GetSignedInUser(context.Background(), query)
 		require.NoError(t, err)
 		require.Equal(t, result.Email, "user1@test.com")
+
+		// Throw errors for invalid user IDs
+		for _, userID := range []int64{-1, 0} {
+			_, err = userStore.GetSignedInUser(context.Background(),
+				&user.GetSignedInUserQuery{
+					OrgID:  users[1].OrgID,
+					UserID: userID}) // zero
+			require.Error(t, err)
+		}
 	})
 
 	t.Run("update user", func(t *testing.T) {