diff --git a/install-dev/upgrade/php/p15017_add_id_shop_to_primary_key.php b/install-dev/upgrade/php/p15017_add_id_shop_to_primary_key.php
index 964da1b6a..c608fb030 100644
--- a/install-dev/upgrade/php/p15017_add_id_shop_to_primary_key.php
+++ b/install-dev/upgrade/php/p15017_add_id_shop_to_primary_key.php
@@ -27,10 +27,21 @@
 
 function p15017_add_id_shop_to_primary_key()
 {
+	// Drop old indexes
+	$old_indexes = array(
+		'category_lang_index' => 'category_lang',
+		'shipper_lang_index' => 'carrier_lang',
+		'product_lang_index' => 'product_lang'
+	);
+	foreach ($old_indexes as $index => $table)
+		if (Db::getInstance()->executeS('SHOW INDEX FROM `'._DB_PREFIX_.$table.'` WHERE Key_name = "'.$index.'"'))
+			Db::getInstance()->execute('ALTER TABLE `'._DB_PREFIX_.$table.'` DROP KEY `'.$index.'`');
+
 	// The former primary keys where set on id_object and id_lang. They must now be set on id_shop too.
 	foreach (array('product', 'category', 'meta', 'carrier') as $table)
 	{
-		Db::getInstance()->execute('ALTER TABLE `'._DB_PREFIX_.$table.'_lang` DROP PRIMARY KEY');
+		if (Db::getInstance()->executeS('SHOW INDEX FROM `'._DB_PREFIX_.$table.'` WHERE Key_name = "PRIMARY"'))
+			Db::getInstance()->execute('ALTER TABLE `'._DB_PREFIX_.$table.'_lang` DROP PRIMARY KEY');
 		Db::getInstance()->execute('ALTER TABLE `'._DB_PREFIX_.$table.'_lang` ADD PRIMARY KEY (`id_'.$table.'`, `id_shop`, `id_lang`)');
 	}