diff --git a/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
index 2190ee5..0a7dc6b 100644
--- a/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
@@ -201,7 +201,7 @@ protected function createTableSql($name, $table) {
     }
     if (isset($table['unique keys']) && is_array($table['unique keys'])) {
       foreach ($table['unique keys'] as $key_name => $key) {
-        $sql_keys[] = 'CONSTRAINT ' . $this->ensureIdentifiersLength($name, $key_name, 'key') . ' UNIQUE (' . implode(', ', $key) . ')';
+        $sql_keys[] = 'CONSTRAINT ' . $this->ensureIdentifiersLength($name, $key_name, 'key') . ' UNIQUE (' . $this->createKeySql($key) . ')';
       }
     }
 
@@ -372,7 +372,7 @@ function getFieldTypeMap() {
     return $map;
   }
 
-  protected function _createKeySql($fields) {
+  protected function createKeySql($fields) {
     $return = array();
     foreach ($fields as $field) {
       if (is_array($field)) {
@@ -559,7 +559,7 @@ function addUniqueKey($table, $name, $fields) {
       throw new SchemaObjectExistsException(t("Cannot add unique key @name to table @table: unique key already exists.", array('@table' => $table, '@name' => $name)));
     }
 
-    $this->connection->query('ALTER TABLE {' . $table . '} ADD CONSTRAINT "' . $this->ensureIdentifiersLength($table, $name, 'key') . '" UNIQUE (' . implode(',', $fields) . ')');
+    $this->connection->query('ALTER TABLE {' . $table . '} ADD CONSTRAINT "' . $this->ensureIdentifiersLength($table, $name, 'key') . '" UNIQUE (' . $this->createKeySql($fields) . ')');
   }
 
   public function dropUniqueKey($table, $name) {
@@ -695,7 +695,7 @@ public function changeField($table, $field, $field_new, $spec, $new_keys = array
 
   protected function _createIndexSql($table, $name, $fields) {
     $query = 'CREATE INDEX "' . $this->ensureIdentifiersLength($table, $name, 'idx') . '" ON {' . $table . '} (';
-    $query .= $this->_createKeySql($fields) . ')';
+    $query .= $this->createKeySql($fields) . ')';
     return $query;
   }