diff --git a/lib/acts_as_taggable_on/tag_list.rb b/lib/acts_as_taggable_on/tag_list.rb
index 6f74fdcc2..c3523d597 100644
--- a/lib/acts_as_taggable_on/tag_list.rb
+++ b/lib/acts_as_taggable_on/tag_list.rb
@@ -149,9 +149,10 @@ def to_s
 
     private
 
-    # Remove whitespace, duplicates, and blanks.
+    # Convert everything to string, remove whitespace, duplicates, and blanks.
     def clean!
       reject!(&:blank?)
+      map!(&:to_s)
       map!(&:strip)
       map! { |tag| tag.mb_chars.downcase.to_s } if ActsAsTaggableOn.force_lowercase
       map!(&:parameterize) if ActsAsTaggableOn.force_parameterize