diff --git a/core/modules/content_moderation/src/Plugin/Validation/Constraint/ModerationStateConstraint.php b/core/modules/content_moderation/src/Plugin/Validation/Constraint/ModerationStateConstraint.php
index c2c373f32fb..eebb06624ca 100644
--- a/core/modules/content_moderation/src/Plugin/Validation/Constraint/ModerationStateConstraint.php
+++ b/core/modules/content_moderation/src/Plugin/Validation/Constraint/ModerationStateConstraint.php
@@ -15,5 +15,6 @@ use Symfony\Component\Validator\Constraint;
 class ModerationStateConstraint extends Constraint {
 
   public $message = 'Invalid state transition from %from to %to';
+  public $invalidStateMessage = 'State %state does not exist on %workflow';
 
 }
diff --git a/core/modules/content_moderation/src/Plugin/Validation/Constraint/ModerationStateConstraintValidator.php b/core/modules/content_moderation/src/Plugin/Validation/Constraint/ModerationStateConstraintValidator.php
index b664c65d259..97ebc9328b0 100644
--- a/core/modules/content_moderation/src/Plugin/Validation/Constraint/ModerationStateConstraintValidator.php
+++ b/core/modules/content_moderation/src/Plugin/Validation/Constraint/ModerationStateConstraintValidator.php
@@ -68,7 +68,7 @@ class ModerationStateConstraintValidator extends ConstraintValidator implements
    * {@inheritdoc}
    */
   public function validate($value, Constraint $constraint) {
-    /** @var \Drupal\Core\Entity\EntityInterface $entity */
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
     $entity = $value->getEntity();
 
     // Ignore entities that are not subject to moderation anyway.
@@ -76,29 +76,43 @@ class ModerationStateConstraintValidator extends ConstraintValidator implements
       return;
     }
 
-    // Ignore entities that are being created for the first time.
-    if ($entity->isNew()) {
-      return;
-    }
-
-    // Ignore entities that are being moderated for the first time, such as
-    // when they existed before moderation was enabled for this entity type.
-    if ($this->isFirstTimeModeration($entity)) {
-      return;
-    }
-
-    $original_entity = $this->moderationInformation->getLatestRevision($entity->getEntityTypeId(), $entity->id());
-    if (!$entity->isDefaultTranslation() && $original_entity->hasTranslation($entity->language()->getId())) {
-      $original_entity = $original_entity->getTranslation($entity->language()->getId());
-    }
-
     $workflow = $this->moderationInformation->getWorkflowForEntity($entity);
-    $new_state = $workflow->getState($entity->moderation_state->value) ?: $workflow->getInitialState();
-    $original_state = $workflow->getState($original_entity->moderation_state->value);
-    // @todo - what if $new_state references something that does not exist or
-    //   is null.
-    if (!$original_state->canTransitionTo($new_state->id())) {
-      $this->context->addViolation($constraint->message, ['%from' => $original_state->label(), '%to' => $new_state->label()]);
+
+    if (!$workflow->hasState($entity->moderation_state->value)) {
+      // If the state we are transitioning to doesn't exist, we can't validate
+      // the transitions for this entity further.
+      $this->context->addViolation($constraint->invalidStateMessage, [
+        '%state' => $entity->moderation_state->value,
+        '%workflow' => $workflow->label(),
+      ]);
+      return;
+    }
+
+    // If a new state is being set and there is an existing state, validate
+    // there is a valid transition between them.
+    if (!$entity->isNew() && !$this->isFirstTimeModeration($entity)) {
+      $original_entity = $this->entityTypeManager->getStorage($entity->getEntityTypeId())->loadRevision($entity->getLoadedRevisionId());
+      if (!$entity->isDefaultTranslation() && $original_entity->hasTranslation($entity->language()->getId())) {
+        $original_entity = $original_entity->getTranslation($entity->language()->getId());
+      }
+
+      // If the state of the original entity doesn't exist on the workflow,
+      // we cannot do any further validation of transitions, because none will
+      // be setup for a state that doesn't exist. Instead allow any state to
+      // take its place.
+      if (!$workflow->hasState($original_entity->moderation_state->value)) {
+        return;
+      }
+
+      $new_state = $workflow->getState($entity->moderation_state->value);
+      $original_state = $workflow->getState($original_entity->moderation_state->value);
+
+      if (!$original_state->canTransitionTo($new_state->id())) {
+        $this->context->addViolation($constraint->message, [
+          '%from' => $original_state->label(),
+          '%to' => $new_state->label()
+        ]);
+      }
     }
   }
 
diff --git a/core/modules/content_moderation/tests/src/Kernel/EntityStateChangeValidationTest.php b/core/modules/content_moderation/tests/src/Kernel/EntityStateChangeValidationTest.php
index 7c4f97d391e..c8ce61b5657 100644
--- a/core/modules/content_moderation/tests/src/Kernel/EntityStateChangeValidationTest.php
+++ b/core/modules/content_moderation/tests/src/Kernel/EntityStateChangeValidationTest.php
@@ -96,6 +96,124 @@ class EntityStateChangeValidationTest extends KernelTestBase {
     $this->assertEquals('Invalid state transition from <em class="placeholder">Draft</em> to <em class="placeholder">Archived</em>', $violations->get(0)->getMessage());
   }
 
+  /**
+   * Test validation with an invalid state.
+   */
+  public function testInvalidState() {
+    $node_type = NodeType::create([
+      'type' => 'example',
+    ]);
+    $node_type->save();
+    $workflow = Workflow::load('editorial');
+    $workflow->getTypePlugin()->addEntityTypeAndBundle('node', 'example');
+    $workflow->save();
+
+    $node = Node::create([
+      'type' => 'example',
+      'title' => 'Test title',
+    ]);
+    $node->moderation_state->value = 'invalid_state';
+    $violations = $node->validate();
+
+    $this->assertCount(1, $violations);
+    $this->assertEquals('State <em class="placeholder">invalid_state</em> does not exist on <em class="placeholder">Editorial workflow</em>', $violations->get(0)->getMessage());
+  }
+
+  /**
+   * Test validation with content that has no initial state or an invalid state.
+   */
+  public function testInvalidStateWithoutExisting() {
+    // Create content without moderation enabled for the content type.
+    $node_type = NodeType::create([
+      'type' => 'example',
+    ]);
+    $node_type->save();
+    $node = Node::create([
+      'type' => 'example',
+      'title' => 'Test title',
+    ]);
+    $node->save();
+
+    // Enable moderation to test validation on existing content, with no
+    // explicit state.
+    $workflow = Workflow::load('editorial');
+    $workflow->addState('deleted_state', 'Deleted state');
+    $workflow->getTypePlugin()->addEntityTypeAndBundle('node', 'example');
+    $workflow->save();
+
+    // Validate the invalid state.
+    $node->moderation_state->value = 'invalid_state';
+    $violations = $node->validate();
+    $this->assertCount(1, $violations);
+
+    // Assign the node to a state we're going to delete.
+    $node->moderation_state->value = 'deleted_state';
+    $node->save();
+
+    // Delete the state so $node->original contains an invalid state when
+    // validating.
+    $workflow->deleteState('deleted_state');
+    $workflow->save();
+    $node->moderation_state->value = 'draft';
+    $violations = $node->validate();
+    $this->assertCount(0, $violations);
+  }
+
+  /**
+   * Test state transition validation with multiple languages.
+   */
+  public function testInvalidStateMultilingual() {
+    ConfigurableLanguage::createFromLangcode('fr')->save();
+    $node_type = NodeType::create([
+      'type' => 'example',
+    ]);
+    $node_type->save();
+
+    $workflow = Workflow::load('editorial');
+    $workflow->getTypePlugin()->addEntityTypeAndBundle('node', 'example');
+    $workflow->save();
+
+    $node = Node::create([
+      'type' => 'example',
+      'title' => 'English Published Node',
+      'langcode' => 'en',
+      'moderation_state' => 'published',
+    ]);
+    $node->save();
+
+    $node_fr = $node->addTranslation('fr');
+    $node_fr->setTitle('French Published Node');
+    $node_fr->save();
+    $this->assertEquals('published', $node_fr->moderation_state->value);
+
+    // Create a forward revision of the original node.
+    $node->moderation_state = 'draft';
+    $node->setNewRevision(TRUE);
+    $node->isDefaultRevision(FALSE);
+    $node->save();
+
+    // For the forward english revision, there should be a violation from draft
+    // to archived.
+    $node->moderation_state = 'archived';
+    $violations = $node->validate();
+    $this->assertCount(1, $violations);
+    $this->assertEquals('Invalid state transition from <em class="placeholder">Draft</em> to <em class="placeholder">Archived</em>', $violations->get(0)->getMessage());
+
+    // From the default french published revision, there should be none.
+    $node_fr = Node::load($node->id())->getTranslation('fr');
+    $this->assertEquals('published', $node_fr->moderation_state->value);
+    $node_fr->moderation_state = 'archived';
+    $violations = $node_fr->validate();
+    $this->assertCount(0, $violations);
+
+    // From the latest french revision, there should also be no violation.
+    $node_fr = $node->getTranslation('fr');
+    $this->assertEquals('published', $node_fr->moderation_state->value);
+    $node_fr->moderation_state = 'archived';
+    $violations = $node_fr->validate();
+    $this->assertCount(0, $violations);
+  }
+
   /**
    * Tests that content without prior moderation information can be moderated.
    */