diff -u b/core/modules/aggregator/src/FeedStorageSchema.php b/core/modules/aggregator/src/FeedStorageSchema.php
--- b/core/modules/aggregator/src/FeedStorageSchema.php
+++ b/core/modules/aggregator/src/FeedStorageSchema.php
@@ -33,7 +33,7 @@
           break;
 
         case 'title':
-          $this->addSharedTableFieldIndex($storage_definition, $schema);
+          $this->addSharedTableFieldIndex($storage_definition, $schema, TRUE);
           break;
       }
     }
diff -u b/core/modules/file/src/FileStorageSchema.php b/core/modules/file/src/FileStorageSchema.php
--- b/core/modules/file/src/FileStorageSchema.php
+++ b/core/modules/file/src/FileStorageSchema.php
@@ -33,7 +33,7 @@
           $this->addSharedTableFieldIndex($storage_definition, $schema, TRUE);
           break;
         case 'uri_hash':
-          $this->addSharedTableFieldUniqueKey($storage_definition, $schema, TRUE);
+          $this->addSharedTableFieldUniqueKey($storage_definition, $schema);
           break;
       }
     }
diff -u b/core/modules/file/src/Tests/SaveTest.php b/core/modules/file/src/Tests/SaveTest.php
--- b/core/modules/file/src/Tests/SaveTest.php
+++ b/core/modules/file/src/Tests/SaveTest.php
@@ -81,11 +81,13 @@
       // Ensure the database URI uniqueness constraint is triggered.
       $uppercase_file_duplicate = File::create($uppercase_values);
       file_put_contents($uppercase_file_duplicate->getFileUri(), 'hello world');
+      $constraint_triggered = NULL;
       try {
         $uppercase_file_duplicate->save();
       }
       catch (EntityStorageException $e) {
-        $exception_triggered = (0 === strpos($e->getCode(), '23'));
+        // SQL error codes for unique constraints begin with 23.
+        $constraint_triggered = (0 === strpos($e->getCode(), '23'));
       }
       $this->assertTrue($exception_triggered, 'SQL uniqueness constraint is triggered');
     }