diff --git a/lib/sinatra/base.rb b/lib/sinatra/base.rb
index 14284f63..fd7a67a6 100644
--- a/lib/sinatra/base.rb
+++ b/lib/sinatra/base.rb
@@ -794,7 +794,7 @@ module Sinatra
         if path.respond_to? :to_str
           special_chars = %w{. + ( )}
           pattern =
-            path.gsub(/((:\w+)|[\*#{special_chars.join}])/) do |match|
+            path.to_str.gsub(/((:\w+)|[\*#{special_chars.join}])/) do |match|
               case match
               when "*"
                 keys << 'splat'