diff --git a/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php
index de73e57..7eb994c 100644
--- a/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php
+++ b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php
@@ -444,18 +444,13 @@ public function onFieldStorageDefinitionDelete(FieldStorageDefinitionInterface $
     try {
       $has_data = $this->storage->countFieldData($storage_definition, TRUE);
 
-      // @todo Add support for deleting bundle fields.
+      // @todo Add support for deleting bundle fields. Bundle field definitions
+      // are also using the \Drupal\Core\Field\BaseFieldDefinition class, but
+      // their isBaseField() method returns FALSE.
       // @see https://www.drupal.org/node/2907780
       if ($storage_definition instanceof BaseFieldDefinition && !$storage_definition->isBaseField() && $has_data) {
         throw new FieldStorageDefinitionUpdateForbiddenException('Unable to delete a field (' . $storage_definition->getName() . ' in ' . $storage_definition->getTargetEntityTypeId() . ' entity) with data that cannot be purged.');
       }
-
-      // If the field storage does not have any data, we can safely delete its
-      // schema.
-      if (!$has_data) {
-        $this->performFieldSchemaOperation('delete', $storage_definition);
-        return;
-      }
     }
     catch (DatabaseExceptionWrapper $e) {
       // This may happen when changing field storage schema, since we are not
@@ -465,7 +460,14 @@ public function onFieldStorageDefinitionDelete(FieldStorageDefinitionInterface $
       return;
     }
 
-    // There's nothing to do if the field storage uses a custom storage.
+    // If the field storage does not have any data, we can safely delete its
+    // schema.
+    if (!$has_data) {
+      $this->performFieldSchemaOperation('delete', $storage_definition);
+      return;
+    }
+
+    // There's nothing else we can do if the field storage has a custom storage.
     if ($storage_definition->hasCustomStorage()) {
       return;
     }
@@ -520,14 +522,15 @@ public function onFieldStorageDefinitionDelete(FieldStorageDefinitionInterface $
       }
       try {
         // Copy the data from the base table.
-        $base_table = $this->entityType->isTranslatable() ? $this->storage->getDataTable() : $this->storage->getBaseTable();
+        $is_translatable = $this->entityType->isTranslatable() && $storage_definition->isTranslatable();
+        $base_table = $is_translatable ? $this->storage->getDataTable() : $this->storage->getBaseTable();
         $this->database->insert($dedicated_table_name)
           ->from($this->getSelectQueryForFieldStorageDeletion($base_table, $shared_table_field_columns, $dedicated_table_field_columns))
           ->execute();
 
         // Copy the data from the revision table.
         if ($this->entityType->isRevisionable()) {
-          $revision_table = $this->entityType->isTranslatable() ? $this->storage->getRevisionDataTable() : $this->storage->getRevisionTable();
+          $revision_table = $is_translatable ? $this->storage->getRevisionDataTable() : $this->storage->getRevisionTable();
           $this->database->insert($dedicated_revision_table_name)
             ->from($this->getSelectQueryForFieldStorageDeletion($revision_table, $shared_table_field_columns, $dedicated_table_field_columns, $base_table))
             ->execute();
@@ -614,7 +617,8 @@ protected function getSelectQueryForFieldStorageDeletion($table_name, array $sha
       $select->addExpression(':langcode', 'langcode', [':langcode' => LanguageInterface::LANGCODE_DEFAULT]);
     }
 
-    // Add the delta column.
+    // Add the delta column and set it to 0 because we are only dealing with
+    // single cardinality fields.
     $select->addExpression(':delta', 'delta', [':delta' => 0]);
 
     // Add all the dynamic field columns.
diff --git a/core/lib/Drupal/Core/Field/BaseFieldDefinition.php b/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
index 5a53eb7..4dbf61e 100644
--- a/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
+++ b/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
@@ -818,7 +818,7 @@ public function getUniqueIdentifier() {
    * {@inheritdoc}
    */
   public function isDeleted() {
-    return isset($this->definition['deleted']) ? (bool) $this->definition['deleted'] : FALSE;
+    return !empty($this->definition['deleted']);
   }
 
   /**