diff --git a/lib/mysql.js b/lib/mysql.js
index 28b980e..39e7322 100644
--- a/lib/mysql.js
+++ b/lib/mysql.js
@@ -20,7 +20,7 @@ var MySQL = function(credentials){
       information_schema.key_column_usage           \
       where table_name = ist.table_name             \
       and constraint_schema = ist.table_schema      \
-      and constraint_name = 'PRIMARY'               \
+      and constraint_name = 'PRIMARY' LIMIT 1       \
     )  as 'pk'                                      \
     from information_schema.tables ist              \
     where table_schema = '" + credentials.database + "'";