diff --git a/activerecord/lib/active_record/associations/preloader.rb b/activerecord/lib/active_record/associations/preloader.rb
index 0848e7afb37f5fafa20d2f9d6b219c82932a1dc5..82bf426b22fcb6b1fd8c013df1b371b4aa9f2a2d 100644
--- a/activerecord/lib/active_record/associations/preloader.rb
+++ b/activerecord/lib/active_record/associations/preloader.rb
@@ -100,7 +100,9 @@ def preload(association)
         case association
         when Hash
           preload_hash(association)
-        when String, Symbol
+        when Symbol
+          preload_one(association)
+        when String
           preload_one(association.to_sym)
         else
           raise ArgumentError, "#{association.inspect} was not recognised for preload"