diff --git a/lib/dynamic_paperclip/attachment.rb b/lib/dynamic_paperclip/attachment.rb
index <HASH>..<HASH> 100644
--- a/lib/dynamic_paperclip/attachment.rb
+++ b/lib/dynamic_paperclip/attachment.rb
@@ -42,7 +42,7 @@ module DynamicPaperclip
 
       url = url(style_name)
 
-      delimiter_char = url.match(/\?.+=/) ? '&' : '?'
+      delimiter_char = url.match(/\?/) ? '&' : '?'
 
       "#{url}#{delimiter_char}s=#{UrlSecurity.generate_hash(style_name)}"
     end
@@ -64,4 +64,4 @@ module DynamicPaperclip
         @dynamic_styles[name.to_sym] = Paperclip::Style.new(name, StyleNaming.style_definition_from_dynamic_style_name(name), self)
       end
   end
-end
\ No newline at end of file
+end
Fix to support the paperclip timestamp param which doesn't have a value.