diff --git a/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
index 7d3ba7ce33..efe618cb1e 100644
--- a/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
@@ -715,7 +715,20 @@ public function findPrimaryKeyColumns($table) {
     if (!$this->tableExists($table)) {
       return FALSE;
     }
-    return $this->connection->query("SELECT array_position(i.indkey, a.attnum) AS position, a.attname FROM pg_index i JOIN pg_attribute a ON a.attrelid = i.indrelid AND a.attnum = ANY(i.indkey) WHERE i.indrelid = '{" . $table . "}'::regclass AND i.indisprimary ORDER BY position")->fetchAllKeyed();
+
+    // Fetch the 'indkey' column from 'pg_index' to figure out the order of the
+    // primary key.
+    // @todo Use 'array_position()' to be able to perform the ordering in SQL
+    //   directly when 9.5 is the minimum  PostgreSQL version.
+    $result = $this->connection->query("SELECT a.attname, i.indkey FROM pg_index i JOIN pg_attribute a ON a.attrelid = i.indrelid AND a.attnum = ANY(i.indkey) WHERE i.indrelid = '{" . $table . "}'::regclass AND i.indisprimary")->fetchAllKeyed();
+    if (!$result) {
+      return [];
+    }
+
+    $order = explode(' ', reset($result));
+    $columns = array_combine($order, array_keys($result));
+    ksort($columns);
+    return array_values($columns);
   }
 
   /**