diff --git a/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php b/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
index c952630..c673009 100644
--- a/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
@@ -395,14 +395,22 @@ public function addField($table, $field, $spec, $keys_new = array()) {
       throw new SchemaObjectExistsException(t("Cannot add field @table.@field: field already exists.", array('@field' => $field, '@table' => $table)));
     }
 
+    // Fields that are part of a PRIMARY KEY can not be added as NOT NULL.
+    $is_primary_key = isset($keys_new['primary key']) && in_array($field, $keys_new['primary key'], TRUE);
+
     $fixnull = FALSE;
-    if (!empty($spec['not null']) && !isset($spec['default'])) {
+    if (!empty($spec['not null']) && !isset($spec['default']) && !$is_primary_key) {
       $fixnull = TRUE;
       $spec['not null'] = FALSE;
     }
     $query = 'ALTER TABLE {' . $table . '} ADD ';
     $query .= $this->createFieldSql($field, $this->processField($spec));
     if ($keys_sql = $this->createKeysSql($keys_new)) {
+      // Make sure to drop the existing primary key before adding a new one.
+      if (isset($keys_new['primary key']) && $this->indexExists($table, 'PRIMARY')) {
+        $query .= ', DROP PRIMARY KEY';
+      }
+
       $query .= ', ADD ' . implode(', ADD ', $keys_sql);
     }
     $this->connection->query($query);
diff --git a/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
index 4a5f404..ac9c2e5 100644
--- a/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
@@ -543,8 +543,11 @@ public function addField($table, $field, $spec, $new_keys = array()) {
       throw new SchemaObjectExistsException(t("Cannot add field @table.@field: field already exists.", array('@field' => $field, '@table' => $table)));
     }
 
+    // Fields that are part of a PRIMARY KEY can not be added as NOT NULL.
+    $is_primary_key = isset($keys_new['primary key']) && in_array($field, $keys_new['primary key'], TRUE);
+
     $fixnull = FALSE;
-    if (!empty($spec['not null']) && !isset($spec['default'])) {
+    if (!empty($spec['not null']) && !isset($spec['default']) && !$is_primary_key) {
       $fixnull = TRUE;
       $spec['not null'] = FALSE;
     }
diff --git a/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php
index 96cea9f..4e5555c 100644
--- a/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php
+++ b/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php
@@ -1018,9 +1018,7 @@ protected function addTableDefaults(&$schema) {
    * @return array
    *   A partial schema array for the base table.
    */
-  protected function processBaseTable(ContentEntityTypeInterface $entity_type, array &$schema) {
-    $this->processIdentifierSchema($schema, $entity_type->getKey('id'));
-  }
+  protected function processBaseTable(ContentEntityTypeInterface $entity_type, array &$schema) { }
 
   /**
    * Processes the gathered schema for a base table.
@@ -1033,9 +1031,7 @@ protected function processBaseTable(ContentEntityTypeInterface $entity_type, arr
    * @return array
    *   A partial schema array for the base table.
    */
-  protected function processRevisionTable(ContentEntityTypeInterface $entity_type, array &$schema) {
-    $this->processIdentifierSchema($schema, $entity_type->getKey('revision'));
-  }
+  protected function processRevisionTable(ContentEntityTypeInterface $entity_type, array &$schema) { }
 
   /**
    * Processes the gathered schema for a base table.
@@ -1157,10 +1153,19 @@ protected function createSharedTableSchema(FieldStorageDefinitionInterface $stor
           $schema[$table_name] = $this->getSharedTableFieldSchema($storage_definition, $table_name, $column_names);
           if (!$only_save) {
             foreach ($schema[$table_name]['fields'] as $name => $specifier) {
+              // Check if the field is part of the primary keys and pass along
+              // this information when adding the field.
+              // @see \Drupal\Core\Database\Schema::addField()
+              $keys_new = [];
+              $entity_schema = $this->getEntitySchema($this->entityType);
+              if (isset($entity_schema[$table_name]['primary key']) && in_array($created_field_name, $entity_schema[$table_name]['primary key'], TRUE)) {
+                $keys_new = ['primary key' => $entity_schema[$table_name]['primary key']];
+              }
+
               // Check if the field exists because it might already have been
               // created as part of the earlier entity type update event.
               if (!$schema_handler->fieldExists($table_name, $name)) {
-                $schema_handler->addField($table_name, $name, $specifier);
+                $schema_handler->addField($table_name, $name, $specifier, $keys_new);
               }
             }
             if (!empty($schema[$table_name]['indexes'])) {
@@ -1650,6 +1655,15 @@ protected function getSharedTableFieldSchema(FieldStorageDefinitionInterface $st
       $schema['foreign keys'] = $this->getFieldForeignKeys($field_name, $field_schema, $column_mapping);
     }
 
+    // Process the 'id' and 'revision' entity keys for the base and revision
+    // tables.
+    if ($field_name === $this->entityType->getKey('id') && $table_name === $this->storage->getBaseTable()) {
+      $this->processIdentifierSchema($schema, $this->entityType->getKey('id'));
+    }
+    if ($field_name === $this->entityType->getKey('revision') && $table_name === $this->storage->getRevisionTable()) {
+      $this->processIdentifierSchema($schema, $this->entityType->getKey('revision'));
+    }
+
     return $schema;
   }
 
@@ -1977,6 +1991,15 @@ protected function hasColumnChanges(FieldStorageDefinitionInterface $storage_def
           $definition_spec = array_intersect_key($definition_schema[$table]['fields'][$name], $keys);
           $stored_spec = array_intersect_key($spec, $keys);
           if ($definition_spec != $stored_spec) {
+            // Prior to Drupal 8.3.0, the last installed schema for the 'id' and
+            // 'revision' fields of all content entity types was storing an
+            // 'int' type instead of 'serial', so we need to explicitly allow
+            // this conversion.
+            // @see system_update_8203()
+            // @see https://www.drupal.org/node/2841291
+            if ($definition_spec['type'] == 'serial' && $stored_spec['type'] == 'int') {
+              return FALSE;
+            }
             return TRUE;
           }
         }
diff --git a/core/modules/system/src/Tests/Update/EntityUpdateTest.php b/core/modules/system/src/Tests/Update/EntityUpdateTest.php
new file mode 100644
index 0000000..8a10b3f
--- /dev/null
+++ b/core/modules/system/src/Tests/Update/EntityUpdateTest.php
@@ -0,0 +1,62 @@
+<?php
+
+namespace Drupal\system\Tests\Update;
+
+/**
+ * Tests the upgrade path for various entity update issues.
+ *
+ * @see https://www.drupal.org/node/2841291
+ *
+ * @group Update
+ */
+class EntityUpdateTest extends UpdatePathTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setDatabaseDumpFiles() {
+    $this->databaseDumpFiles = [
+      __DIR__ . '/../../../../system/tests/fixtures/update/drupal-8.bare.standard.php.gz',
+    ];
+  }
+
+  /**
+   * Tests system_update_8203().
+   */
+  public function testSystemUpdate8203() {
+    // The installed field storage schema is wrong before running the update.
+    $key_value_store = \Drupal::keyValue('entity.storage_schema.sql');
+    $id_schema = $key_value_store->get('node.field_schema_data.nid', []);
+    $revision_id_schema = $key_value_store->get('node.field_schema_data.vid', []);
+
+    $this->assertEqual('int', $id_schema['node']['fields']['nid']['type']);
+    $this->assertEqual('int', $id_schema['node_revision']['fields']['nid']['type']);
+    $this->assertEqual('int', $revision_id_schema['node']['fields']['vid']['type']);
+    $this->assertEqual('int', $revision_id_schema['node_revision']['fields']['vid']['type']);
+
+    $this->runUpdates();
+
+    // Now check that the schema has been corrected.
+    $id_schema = $key_value_store->get('node.field_schema_data.nid', []);
+    $revision_id_schema = $key_value_store->get('node.field_schema_data.vid', []);
+
+    $this->assertEqual('serial', $id_schema['node']['fields']['nid']['type']);
+    $this->assertEqual('int', $id_schema['node_revision']['fields']['nid']['type']);
+    $this->assertEqual('int', $revision_id_schema['node']['fields']['vid']['type']);
+    $this->assertEqual('serial', $revision_id_schema['node_revision']['fields']['vid']['type']);
+
+    // Check that creating and loading a node still works as expected.
+    $node_storage = \Drupal::entityTypeManager()->getStorage('node');
+    $node = $node_storage->create([
+      'title' => 'Test update',
+      'type' => 'article',
+    ]);
+    $node->save();
+
+    $node_storage->resetCache();
+
+    $node = $node_storage->load($node->id());
+    $this->assertEqual('Test update', $node->label());
+  }
+
+}
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index f1fcfba..f3e56ca 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -13,6 +13,7 @@
 use Drupal\Core\Url;
 use Drupal\Core\Database\Database;
 use Drupal\Core\DrupalKernel;
+use Drupal\Core\Entity\Sql\SqlEntityStorageInterface;
 use Drupal\Core\Site\Settings;
 use Drupal\Core\StreamWrapper\PrivateStream;
 use Drupal\Core\StreamWrapper\PublicStream;
@@ -1786,6 +1787,41 @@ function system_update_8202() {
  */
 
 /**
+ * @addtogroup updates-8.2.6
+ * @{
+ */
+
+/**
+ * Correct the last installed storage schema for every entity type's ID and
+ * revision fields.
+ */
+function system_update_8203() {
+  $entity_type_manager = \Drupal::entityTypeManager();
+  $definition_update_manager = \Drupal::entityDefinitionUpdateManager();
+  /** @var \Drupal\Core\Entity\EntityLastInstalledSchemaRepositoryInterface $entity_last_installed_schema_respository */
+  $entity_last_installed_schema_respository = \Drupal::service('entity.last_installed_schema.repository');
+
+  foreach ($entity_type_manager->getDefinitions() as $entity_type_id => $entity_type) {
+    $storage = $entity_type_manager->getStorage($entity_type_id);
+    if ($storage instanceof SqlEntityStorageInterface) {
+      $field_names_to_update = [$entity_type->getKey('id')];
+      if ($entity_type->isRevisionable()) {
+        $field_names_to_update[] = $entity_type->getKey('revision');
+      }
+      foreach ($entity_last_installed_schema_respository->getLastInstalledFieldStorageDefinitions($entity_type_id) as $field_name => $field_definition) {
+        if (in_array($field_definition->getName(), $field_names_to_update)) {
+          $definition_update_manager->updateFieldStorageDefinition($field_definition);
+        }
+      }
+    }
+  }
+}
+
+/**
+ * @} End of "addtogroup updates-8.2.6".
+ */
+
+/**
  * @addtogroup updates-8.3.0
  * @{
  */
diff --git a/core/tests/Drupal/KernelTests/Core/Database/SchemaTest.php b/core/tests/Drupal/KernelTests/Core/Database/SchemaTest.php
index 8641fd3..1583e5c 100644
--- a/core/tests/Drupal/KernelTests/Core/Database/SchemaTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Database/SchemaTest.php
@@ -143,6 +143,24 @@ function testSchema() {
     $count = db_query('SELECT COUNT(*) FROM {test_table}')->fetchField();
     $this->assertEqual($count, 2, 'There were two rows.');
 
+    // Test adding a serial field to an existing table.
+    db_drop_table('test_table');
+    db_create_table('test_table', $table_specification);
+    db_field_set_default('test_table', 'test_field', 0);
+    db_add_field('test_table', 'test_serial', ['type' => 'serial', 'not null' => TRUE], ['primary key' => ['test_serial']]);
+
+    $this->assertTrue($this->tryInsert(), 'Insert with a serial succeeded.');
+    $max1 = db_query('SELECT MAX(test_serial) FROM {test_table}')->fetchField();
+    $this->assertTrue($this->tryInsert(), 'Insert with a serial succeeded.');
+    $max2 = db_query('SELECT MAX(test_serial) FROM {test_table}')->fetchField();
+    $this->assertTrue($max2 > $max1, 'The serial is monotone.');
+
+    $count = db_query('SELECT COUNT(*) FROM {test_table}')->fetchField();
+    $this->assertEqual($count, 2, 'There were two rows.');
+
+    // Test adding a new column and form a composite primary key with it.
+    db_add_field('test_table', 'test_composite_primary_key', ['type' => 'int', 'not null' => TRUE], ['primary key' => ['test_serial', 'test_composite_primary_key']]);
+
     // Test renaming of keys and constraints.
     db_drop_table('test_table');
     $table_specification = array(
diff --git a/core/tests/Drupal/KernelTests/Core/Entity/EntityDefinitionUpdateTest.php b/core/tests/Drupal/KernelTests/Core/Entity/EntityDefinitionUpdateTest.php
index e49ee7e..e716b70 100644
--- a/core/tests/Drupal/KernelTests/Core/Entity/EntityDefinitionUpdateTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Entity/EntityDefinitionUpdateTest.php
@@ -810,4 +810,51 @@ public function testLongNameFieldIndexes() {
     $this->assertFalse($this->entityDefinitionUpdateManager->needsUpdates(), 'Entity and field schema data are correctly detected.');
   }
 
+  /**
+   * Checks that updating the main identifier field ('id') is correctly handled.
+   */
+  public function testUpdateIdentifierField() {
+    // Get the storage definition for an entity identifier, the 'id' field.
+    $storage_definition = $this->entityDefinitionUpdateManager->getFieldStorageDefinition('id', 'entity_test_update');
+
+    // Update the storage definition without any changes.
+    $this->entityDefinitionUpdateManager->updateFieldStorageDefinition($storage_definition);
+
+    // Check that creating, saving and loading an entity still works.
+    $storage = $this->entityManager->getStorage('entity_test_update');
+
+    $entity = $storage->create();
+    $entity->save();
+
+    $storage->resetCache();
+    $this->assertNotNull($storage->load($entity->id()));
+  }
+
+  /**
+   * Check that updating the revision identifier field is correctly handled.
+   */
+  public function testUpdateRevisionIdentifierField() {
+    $this->updateEntityTypeToRevisionable();
+    $this->entityDefinitionUpdateManager->applyUpdates();
+
+    // Get the storage definition for the revision identifier, the 'revision_id'
+    // field.
+    $storage_definition = $this->entityDefinitionUpdateManager->getFieldStorageDefinition('revision_id', 'entity_test_update');
+
+    // Update the storage definition without any changes.
+    $this->entityDefinitionUpdateManager->updateFieldStorageDefinition($storage_definition);
+
+    // Check that creating and saving an entity still works.
+    $this->entityManager->getStorage('entity_test_update')->create()->save();
+
+    // Check that creating, saving and loading an entity still works.
+    $storage = $this->entityManager->getStorage('entity_test_update');
+
+    $entity = $storage->create();
+    $entity->save();
+
+    $storage->resetCache();
+    $this->assertNotNull($storage->loadRevision($entity->getRevisionId()));
+  }
+
 }
diff --git a/core/tests/Drupal/KernelTests/Core/Entity/EntitySchemaTest.php b/core/tests/Drupal/KernelTests/Core/Entity/EntitySchemaTest.php
index fdf72df..e01d912 100644
--- a/core/tests/Drupal/KernelTests/Core/Entity/EntitySchemaTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Entity/EntitySchemaTest.php
@@ -5,9 +5,9 @@
 use Drupal\Component\Utility\SafeMarkup;
 
 /**
- * Tests adding a custom bundle field.
+ * Tests the default entity storage schema handler.
  *
- * @group system
+ * @group Entity
  */
 class EntitySchemaTest extends EntityKernelTestBase {
 
@@ -188,4 +188,63 @@ public function testCleanUpStorageDefinition() {
     $this->assertEqual($entity_type_id_count, 0, 'After uninstalling entity_test module the schema should not contains fields from entities provided by the module.');
   }
 
+  /**
+   * Tests the installed storage schema for identifier fields.
+   */
+  public function testIdentifierSchema() {
+    $this->installEntitySchema('entity_test_rev');
+
+    $key_value_store = \Drupal::keyValue('entity.storage_schema.sql');
+    $id_schema = $key_value_store->get('entity_test_rev.field_schema_data.id', []);
+    $revision_id_schema = $key_value_store->get('entity_test_rev.field_schema_data.revision_id', []);
+
+    $expected_id_schema = [
+      'entity_test_rev' => [
+        'fields' => [
+          'id' => [
+            'type' => 'serial',
+            'unsigned' => TRUE,
+            'size' => 'normal',
+            'not null' => TRUE,
+          ],
+        ],
+      ],
+      'entity_test_rev_revision' => [
+        'fields' => [
+          'id' => [
+            'type' => 'int',
+            'unsigned' => TRUE,
+            'size' => 'normal',
+            'not null' => TRUE,
+          ],
+        ],
+      ],
+    ];
+    $this->assertEquals($expected_id_schema, $id_schema);
+
+    $expected_revision_id_schema = [
+      'entity_test_rev' => [
+        'fields' => [
+          'revision_id' => [
+            'type' => 'int',
+            'unsigned' => TRUE,
+            'size' => 'normal',
+            'not null' => FALSE,
+          ],
+        ],
+      ],
+      'entity_test_rev_revision' => [
+        'fields' => [
+          'revision_id' => [
+            'type' => 'serial',
+            'unsigned' => TRUE,
+            'size' => 'normal',
+            'not null' => TRUE,
+          ],
+        ],
+      ],
+    ];
+    $this->assertEquals($expected_revision_id_schema, $revision_id_schema);
+  }
+
 }
diff --git a/core/tests/Drupal/Tests/Core/Entity/Sql/SqlContentEntityStorageSchemaTest.php b/core/tests/Drupal/Tests/Core/Entity/Sql/SqlContentEntityStorageSchemaTest.php
index 1ce87c5..b0f2948 100644
--- a/core/tests/Drupal/Tests/Core/Entity/Sql/SqlContentEntityStorageSchemaTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/Sql/SqlContentEntityStorageSchemaTest.php
@@ -397,7 +397,7 @@ public function testGetSchemaRevisionable() {
       ),
     ));
 
-    $this->storage->expects($this->exactly(2))
+    $this->storage->expects($this->atLeastOnce())
       ->method('getRevisionTable')
       ->will($this->returnValue('entity_test_revision'));
 
@@ -604,7 +604,7 @@ public function testGetSchemaRevisionableTranslatable() {
       ),
     ));
 
-    $this->storage->expects($this->exactly(3))
+    $this->storage->expects($this->atLeastOnce())
       ->method('getRevisionTable')
       ->will($this->returnValue('entity_test_revision'));
     $this->storage->expects($this->once())