diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 0b5e9b4fb207c0ae6152866b3aa100822079565a..8ccc62c9d12c02ce5c8f3193c78f98ed7da087df 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -121,8 +121,10 @@ def custom_join_sql(*joins)
         when Hash, Array, Symbol
           if array_of_strings?(join)
             join_string = join.join(' ')
-            arel = arel.join(join_string)
+            arel = arel.join(Arel::SqlLiteral.new(join_string))
           end
+        when String
+          arel = arel.join(Arel::SqlLiteral.new(join))
         else
           arel = arel.join(join)
         end