diff --git a/core/modules/content_translation/src/Plugin/Validation/Constraint/ContentTranslationSynchronizedFieldsConstraintValidator.php b/core/modules/content_translation/src/Plugin/Validation/Constraint/ContentTranslationSynchronizedFieldsConstraintValidator.php
index 35e4358892..f46ef526ac 100644
--- a/core/modules/content_translation/src/Plugin/Validation/Constraint/ContentTranslationSynchronizedFieldsConstraintValidator.php
+++ b/core/modules/content_translation/src/Plugin/Validation/Constraint/ContentTranslationSynchronizedFieldsConstraintValidator.php
@@ -28,6 +28,7 @@
  *   new default revision.
  *
  * @see \Drupal\content_translation\Plugin\Validation\Constraint\ContentTranslationSynchronizedFieldsConstraint
+ * @see \Drupal\Core\Entity\Plugin\Validation\Constraint\EntityUntranslatableFieldsConstraintValidator
  *
  * @internal
  */
@@ -96,12 +97,6 @@ public function validate($value, Constraint $constraint) {
     if ($entity->isDefaultRevision() && !$entity->isDefaultTranslationAffectedOnly()) {
       return;
     }
-    // When changes to untranslatable fields are configured to affect only the
-    // default revision translation, we always allow changes in default
-    // translation.
-    if ($entity->isDefaultTranslation() && $entity->isDefaultTranslationAffectedOnly()) {
-      return;
-    }
     $entity_type_id = $entity->getEntityTypeId();
     if (!$this->contentTranslationManager->isEnabled($entity_type_id, $entity->bundle())) {
       return;
@@ -114,29 +109,18 @@ public function validate($value, Constraint $constraint) {
     /** @var \Drupal\Core\Entity\ContentEntityInterface $original */
     $original = $this->getOriginalEntity($entity);
     $original_translation = $this->getOriginalTranslation($entity, $original);
-    $has_changes = $this->hasSynchronizedPropertyChanges($entity, $original_translation, $synchronized_properties);
-
-    if ($entity->isDefaultTranslationAffectedOnly()) {
-      if ($has_changes) {
-        $this->context->addViolation($constraint->defaultTranslationMessage);
-      }
-      else {
-        $active_langcode = $entity->language()->getId();
+    if ($this->hasSynchronizedPropertyChanges($entity, $original_translation, $synchronized_properties)) {
+      if ($entity->isDefaultTranslationAffectedOnly()) {
         foreach ($entity->getTranslationLanguages(FALSE) as $langcode => $language) {
-          // We already checked the active translation above.
-          if ($langcode !== $active_langcode) {
-            $translation = $entity->getTranslation($langcode);
-            $original_translation = $this->getOriginalTranslation($entity, $original);
-            if ($this->hasSynchronizedPropertyChanges($translation, $original_translation, $synchronized_properties)) {
-              $this->context->addViolation($constraint->defaultTranslationMessage);
-              break;
-            }
+          if ($entity->getTranslation($langcode)->hasTranslationChanges()) {
+            $this->context->addViolation($constraint->defaultTranslationMessage);
+            break;
           }
         }
       }
-    }
-    elseif ($has_changes) {
-      $this->context->addViolation($constraint->defaultRevisionMessage);
+      else {
+        $this->context->addViolation($constraint->defaultRevisionMessage);
+      }
     }
   }
 
@@ -164,6 +148,8 @@ protected function hasSynchronizedPropertyChanges(ContentEntityInterface $entity
           return TRUE;
         }
         foreach ($items as $delta => $item) {
+          // @todo This loose comparison is not fully reliable. Revisit this
+          //   after https://www.drupal.org/project/drupal/issues/xxx.
           if ($items[$delta][$property] != $original_items[$delta][$property]) {
             return TRUE;
           }
diff --git a/core/modules/content_translation/tests/src/Kernel/ContentTranslationFieldSyncValidationTest.php b/core/modules/content_translation/tests/src/Kernel/ContentTranslationFieldSyncValidationTest.php
index a0d73b4125..4c75e62785 100644
--- a/core/modules/content_translation/tests/src/Kernel/ContentTranslationFieldSyncValidationTest.php
+++ b/core/modules/content_translation/tests/src/Kernel/ContentTranslationFieldSyncValidationTest.php
@@ -308,6 +308,30 @@ public function testPendingRevisionValidation() {
     $this->assertEmpty($violations);
     $this->storage->save($it_revision);
     $this->assertLatestRevisionFieldValues($entity_id, [20, 4, 4, 'Alt 4 EN', 'Alt 6 IT']);
+
+    // Check that we are not allowed to perform changes to multiple translations
+    // in pending revisions when synchronized properties are involved.
+    $this->setUntranslatableFieldWidgetsDisplay(FALSE);
+    $entity = $this->saveNewEntity();
+    $entity_id = $entity->id();
+    $this->assertLatestRevisionFieldValues($entity_id, [21, 1, 1, 'Alt 1 EN']);
+
+    $it_translation = $entity->addTranslation('it', $entity->toArray());
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $it_revision */
+    $it_revision = $this->createRevision($it_translation);
+    $metadata = $this->contentTranslationManager->getTranslationMetadata($it_revision);
+    $metadata->setSource('en');
+    $it_revision->get($this->fieldName)->alt = 'Alt 2 IT';
+    $violations = $it_revision->validate();
+    $this->assertEmpty($violations);
+    $this->storage->save($it_revision);
+    $this->assertLatestRevisionFieldValues($entity_id, [22, 1, 1, 'Alt 1 EN', 'Alt 2 IT']);
+
+    $en_revision = $this->createRevision($entity, FALSE);
+    $en_revision->get($this->fieldName)->target_id = 2;
+    $en_revision->getTranslation('it')->get($this->fieldName)->alt = 'Alt 3 IT';
+    $violations = $en_revision->validate();
+    $this->assertViolations($violations);
   }
 
   /**