diff --git a/lib/shoulda/matchers/active_record/association_matcher.rb b/lib/shoulda/matchers/active_record/association_matcher.rb
index 771bd1dd..251c9049 100644
--- a/lib/shoulda/matchers/active_record/association_matcher.rb
+++ b/lib/shoulda/matchers/active_record/association_matcher.rb
@@ -191,7 +191,7 @@ module Shoulda # :nodoc:
         end
 
         def foreign_key
-          reflection.primary_key_name
+          reflection.respond_to?(:foreign_key) ? reflection.foreign_key : reflection.primary_key_name
         end
 
         def through?