diff --git a/pg4wp/core.php b/pg4wp/core.php
index 72d2a75..fa45e3b 100644
--- a/pg4wp/core.php
+++ b/pg4wp/core.php
@@ -9,6 +9,17 @@
 * This file does all the initialisation tasks
 */
 
+// This is required by class-wpdb so we must load it first
+require_once ABSPATH . '/wp-includes/cache.php';
+require_once ABSPATH . '/wp-includes/l10n.php';
+
+if (!function_exists('wpsql_is_resource')) {
+    function wpsql_is_resource($object)
+    {
+        return $object !== false && $object !== null;
+    }
+}
+
 // Logs are put in the pg4wp directory
 define( 'PG4WP_LOG', PG4WP_ROOT.'/logs/');
 // Check if the logs directory is needed and exists or create it if possible
@@ -26,13 +37,22 @@
 	'class wpdb'	=> 'class wpdb2',
 	'new wpdb'	=> 'new wpdb2',
 	'mysql_'	=> 'wpsql_',
+	'is_resource'	=> 'wpsql_is_resource',
 	'<?php'		=> '',
 	'?>'		=> '',
 );
+
 // Ensure class uses the replaced mysql_ functions rather than mysqli_
-define( 'WP_USE_EXT_MYSQL', true);
-eval( str_replace( array_keys($replaces), array_values($replaces), file_get_contents(ABSPATH.'/wp-includes/wp-db.php')));
+if (!defined('WP_USE_EXT_MYSQL')) {
+	define('WP_USE_EXT_MYSQL', true);
+}
+if (WP_USE_EXT_MYSQL != true) {
+	throw new \Exception("PG4SQL CANNOT BE ENABLED WITH MYSQLI, REMOVE ANY WP_USE_EXT_MYSQL configuration");
+}
+
+eval(str_replace(array_keys($replaces), array_values($replaces), file_get_contents(ABSPATH . '/wp-includes/class-wpdb.php')));
 
 // Create wpdb object if not already done
-if (! isset($wpdb) && defined('DB_USER'))
+if (! isset($wpdb) && defined('DB_USER')) {
 	$wpdb = new wpdb2( DB_USER, DB_PASSWORD, DB_NAME, DB_HOST );
+}
\ No newline at end of file
diff --git a/pg4wp/db.php b/pg4wp/db.php
index 798e715..fef6b0a 100644
--- a/pg4wp/db.php
+++ b/pg4wp/db.php
@@ -9,32 +9,43 @@
 License: GPLv2 or newer.
 */
 
-if( !defined('PG4WP_ROOT'))
-{
-// You can choose the driver to load here
-define('DB_DRIVER', 'pgsql'); // 'pgsql' or 'mysql' are supported for now
+// Ensure we only load this config once
+if(!defined('PG4WP_ROOT')) {
 
-// Set this to 'true' and check that `pg4wp` is writable if you want debug logs to be written
-define( 'PG4WP_DEBUG', false);
-// If you just want to log queries that generate errors, leave PG4WP_DEBUG to "false"
-// and set this to true
-define( 'PG4WP_LOG_ERRORS', true);
+    // You can choose the driver to load here
+    if (!defined('DB_DRIVER')) {
+        define('DB_DRIVER', pgsql);
+    }
 
-// If you want to allow insecure configuration (from the author point of view) to work with PG4WP,
-// change this to true
-define( 'PG4WP_INSECURE', false);
+    // Set this to 'true' and check that `pg4wp` is writable if you want debug logs to be written
+    if (!defined('PG4WP_DEBUG')) {
+        define('PG4WP_DEBUG', false);
+    }
 
-// This defines the directory where PG4WP files are loaded from
-//   3 places checked : wp-content, wp-content/plugins and the base directory
-if( file_exists( ABSPATH.'/wp-content/pg4wp'))
-	define( 'PG4WP_ROOT', ABSPATH.'/wp-content/pg4wp');
-else if( file_exists( ABSPATH.'/wp-content/plugins/pg4wp'))
-	define( 'PG4WP_ROOT', ABSPATH.'/wp-content/plugins/pg4wp');
-else if( file_exists( ABSPATH.'/pg4wp'))
-	define( 'PG4WP_ROOT', ABSPATH.'/pg4wp');
-else
-	die('PG4WP file directory not found');
+    if (!defined('PG4WP_LOG_ERRORS')) {
+        // If you just want to log queries that generate errors, leave PG4WP_DEBUG to "false"
+        // and set this to true
+        define('PG4WP_LOG_ERRORS', true);
+    }
 
-// Here happens all the magic
-require_once( PG4WP_ROOT.'/core.php');
+    if (!defined('PG4WP_INSECURE')) {
+        // If you want to allow insecure configuration (from the author point of view) to work with PG4WP,
+        // change this to true
+        define('PG4WP_INSECURE', false);
+    }
+
+    // This defines the directory where PG4WP files are loaded from
+    //   3 places checked : wp-content, wp-content/plugins and the base directory
+    if(file_exists(ABSPATH . '/wp-content/pg4wp')) {
+        define('PG4WP_ROOT', ABSPATH . '/wp-content/pg4wp');
+    } elseif(file_exists(ABSPATH . '/wp-content/plugins/pg4wp')) {
+        define('PG4WP_ROOT', ABSPATH . '/wp-content/plugins/pg4wp');
+    } elseif(file_exists(ABSPATH . '/pg4wp')) {
+        define('PG4WP_ROOT', ABSPATH . '/pg4wp');
+    } else {
+        die('PG4WP file directory not found');
+    }
+
+    // Here happens all the magic
+    require_once(PG4WP_ROOT . '/core.php');
 } // Protection against multiple loading