diff --git a/pkg/controller/scheduler.go b/pkg/controller/scheduler.go
index 5b3de8ed..a3acba6c 100644
--- a/pkg/controller/scheduler.go
+++ b/pkg/controller/scheduler.go
@@ -301,7 +301,7 @@ func (c *Controller) advanceCanary(name string, namespace string) {
 				// instead of rolling back traffic to the unhealthy primary
 				if cd.Status.Phase == flaggerv1.CanaryPhasePromoting ||
 					cd.Status.Phase == flaggerv1.CanaryPhaseFinalising {
-					c.handleFailedPromotion(cd, canaryController, err)
+					c.handleFailedPromotion(cd, canaryController, meshRouter, err)
 				} else {
 					c.rollback(cd, canaryController, meshRouter, scalerReconciler)
 				}
@@ -997,14 +997,28 @@ func (c *Controller) rollback(canary *flaggerv1.Canary, canaryController canary.
 }
 
 // handleFailedPromotion marks the rollout as failed when the primary is unhealthy
-// during promotion, without scaling the canary down or routing to the primary.
-func (c *Controller) handleFailedPromotion(canary *flaggerv1.Canary, canaryController canary.Controller, err error) {
+// during promotion and routes all traffic back to the canary, the only healthy
+// copy of the new revision. Traffic may already have been shifted to the primary
+// by runPromotionTrafficShift, so it must be moved back explicitly.
+func (c *Controller) handleFailedPromotion(canary *flaggerv1.Canary, canaryController canary.Controller,
+	meshRouter router.Interface, err error) {
 	c.recordEventWarningf(canary, "Promotion of %s.%s failed, primary not ready: %v",
 		canary.Spec.TargetRef.Name, canary.Namespace, err)
 	c.alert(canary, fmt.Sprintf("Promotion failed, primary not ready: %v", err),
 		false, flaggerv1.SeverityError)
 
-	if err := canaryController.SetStatusPhase(canary, flaggerv1.CanaryPhaseFailed); err != nil {
+	// route all traffic to the canary, off the unhealthy primary
+	primaryWeight := 0
+	canaryWeight := c.totalWeight(canary)
+	if err := meshRouter.SetRoutes(canary, primaryWeight, canaryWeight, false); err != nil {
+		c.recordEventWarningf(canary, "%v", err)
+		return
+	}
+	c.recorder.SetWeight(canary, primaryWeight, canaryWeight)
+
+	// mark as failed while reporting the weight that matches the routing
+	if err := canaryController.SyncStatus(canary, flaggerv1.CanaryStatus{
+		Phase: flaggerv1.CanaryPhaseFailed, CanaryWeight: canaryWeight}); err != nil {
 		c.logger.With("canary", fmt.Sprintf("%s.%s", canary.Name, canary.Namespace)).Errorf("%v", err)
 		return
 	}
diff --git a/pkg/controller/scheduler_deployment_test.go b/pkg/controller/scheduler_deployment_test.go
index 9e7c5704..47bce0c5 100644
--- a/pkg/controller/scheduler_deployment_test.go
+++ b/pkg/controller/scheduler_deployment_test.go
@@ -165,16 +165,76 @@ func TestScheduler_DeploymentPromotionPrimaryNotReady(t *testing.T) {
 	require.NotNil(t, canaryDep.Spec.Replicas)
 	assert.Equal(t, canaryReplicas, *canaryDep.Spec.Replicas, "canary must not be scaled to zero when promotion fails")
 
-	// traffic must NOT be shifted entirely onto the broken primary
+	// traffic must be routed to the healthy canary, off the broken primary
 	primaryWeight, canaryWeight, _, err := mocks.router.GetRoutes(mocks.canary)
 	require.NoError(t, err)
-	assert.NotEqual(t, 100, primaryWeight, "traffic must not be routed entirely to the unhealthy primary")
-	assert.Greater(t, canaryWeight, 0, "canary must keep serving traffic when promotion fails")
+	assert.Equal(t, 0, primaryWeight, "no traffic must remain on the unhealthy primary")
+	assert.Equal(t, 100, canaryWeight, "all traffic must be routed to the healthy canary")
 
 	// the rollout is reported as failed so it stops advancing and alerts
 	c, err := mocks.flaggerClient.FlaggerV1beta1().Canaries("default").Get(context.TODO(), "podinfo", metav1.GetOptions{})
 	require.NoError(t, err)
 	assert.Equal(t, flaggerv1.CanaryPhaseFailed, c.Status.Phase)
+	assert.Equal(t, 100, c.Status.CanaryWeight, "reported canary weight must match the traffic on the canary")
+}
+
+// when the primary fails after promotion traffic has already been shifted to it
+// (Finalising phase), traffic must be routed back to the healthy canary (#1898)
+func TestScheduler_DeploymentPromotionFailedAfterTrafficShift(t *testing.T) {
+	mocks := newDeploymentFixture(nil)
+
+	// initializing
+	mocks.ctrl.advanceCanary("podinfo", "default")
+	mocks.makePrimaryReady(t)
+
+	// initialized
+	mocks.ctrl.advanceCanary("podinfo", "default")
+
+	// update
+	dep2 := newDeploymentTestDeploymentV2()
+	_, err := mocks.kubeClient.AppsV1().Deployments("default").Update(context.TODO(), dep2, metav1.UpdateOptions{})
+	require.NoError(t, err)
+
+	// detect changes -> progressing, canary scaled up
+	mocks.ctrl.advanceCanary("podinfo", "default")
+	mocks.makeCanaryReady(t)
+
+	canaryDep, err := mocks.kubeClient.AppsV1().Deployments("default").Get(context.TODO(), "podinfo", metav1.GetOptions{})
+	require.NoError(t, err)
+	require.NotNil(t, canaryDep.Spec.Replicas)
+	canaryReplicas := *canaryDep.Spec.Replicas
+	require.Greater(t, canaryReplicas, int32(0))
+
+	// simulate: promotion already shifted all traffic to the primary (Finalising)
+	cd, err := mocks.flaggerClient.FlaggerV1beta1().Canaries("default").Get(context.TODO(), "podinfo", metav1.GetOptions{})
+	require.NoError(t, err)
+	err = mocks.deployer.SetStatusPhase(cd, flaggerv1.CanaryPhaseFinalising)
+	require.NoError(t, err)
+	require.NoError(t, mocks.router.SetRoutes(mocks.canary, 100, 0, false))
+
+	// the promoted primary then fails to stay ready
+	mocks.makePrimaryNotReady(t)
+
+	// advance: Flagger observes the primary is stuck
+	mocks.ctrl.advanceCanary("podinfo", "default")
+
+	// traffic must be routed back to the healthy canary, off the broken primary
+	primaryWeight, canaryWeight, _, err := mocks.router.GetRoutes(mocks.canary)
+	require.NoError(t, err)
+	assert.Equal(t, 0, primaryWeight, "no traffic must remain on the unhealthy primary")
+	assert.Equal(t, 100, canaryWeight, "all traffic must be routed to the healthy canary")
+
+	// the canary must not be scaled to zero
+	canaryDep, err = mocks.kubeClient.AppsV1().Deployments("default").Get(context.TODO(), "podinfo", metav1.GetOptions{})
+	require.NoError(t, err)
+	require.NotNil(t, canaryDep.Spec.Replicas)
+	assert.Equal(t, canaryReplicas, *canaryDep.Spec.Replicas, "canary must not be scaled to zero when promotion fails")
+
+	// reported canary weight must match the routing (not zeroed)
+	c, err := mocks.flaggerClient.FlaggerV1beta1().Canaries("default").Get(context.TODO(), "podinfo", metav1.GetOptions{})
+	require.NoError(t, err)
+	assert.Equal(t, flaggerv1.CanaryPhaseFailed, c.Status.Phase)
+	assert.Equal(t, 100, c.Status.CanaryWeight, "reported canary weight must match the traffic on the canary")
 }
 
 func TestScheduler_DeploymentSkipAnalysis(t *testing.T) {