diff --git a/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php
index 2a486b1043..af8f46b153 100644
--- a/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php
+++ b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php
@@ -1452,7 +1452,24 @@ protected function deleteSharedTableSchema(FieldStorageDefinitionInterface $stor
         if ($field_name == $deleted_field_name) {
           $schema = $this->getSharedTableFieldSchema($storage_definition, $table_name, $column_names);
 
-          // Drop indexes and unique keys first.
+          // Drop the primary key, indexes and unique keys first.
+          // The entity schema needs to be checked because the field schema is
+          // potentially incomplete.
+          // @todo Remove this in
+          //   https://www.drupal.org/project/drupal/issues/2929120
+          $entity_schema = $this->getEntitySchema($this->entityType);
+          if (array_intersect($column_names, $entity_schema[$table_name]['primary key'])) {
+            // Dropping a primary key must not leave a serial key, so we need to
+            // change any serial field to integer first.
+            foreach ($entity_schema[$table_name]['primary key'] as $column_name) {
+              if ($entity_schema[$table_name]['fields'][$column_name]['type'] === 'serial') {
+                $field_schema = $entity_schema[$table_name]['fields'][$column_name];
+                $field_schema['type'] = 'int';
+                $schema_handler->changeField($table_name, $column_name, $column_name, $field_schema);
+              }
+            }
+            $schema_handler->dropPrimaryKey($table_name);
+          }
           if (!empty($schema['indexes'])) {
             foreach ($schema['indexes'] as $name => $specifier) {
               $schema_handler->dropIndex($table_name, $name);