diff --git a/lib/rack/utils.rb b/lib/rack/utils.rb
index 2306563d8..fab2c49d4 100644
--- a/lib/rack/utils.rb
+++ b/lib/rack/utils.rb
@@ -483,7 +483,7 @@ def self.parse_multipart(env)
                 dispparm = /;\s*(#{token})=("(?:\\"|[^"])*"|#{token})*/
 
                 rfc2183 = /^#{condisp}(#{dispparm})+$/i
-                broken_quoted = /^#{condisp}.*;\sfilename="(.*?)"(?:\s*$|\s*;\s*\w+=)/i
+                broken_quoted = /^#{condisp}.*;\sfilename="(.*?)"(?:\s*$|\s*;\s*#{token}=)/i
                 broken_unquoted = /^#{condisp}.*;\sfilename=(#{token})/i
 
                 if head =~ rfc2183