diff --git a/actionpack/lib/action_dispatch/journey/path/pattern.rb b/actionpack/lib/action_dispatch/journey/path/pattern.rb
index deb20990b9..6f06215be7 100644
--- a/actionpack/lib/action_dispatch/journey/path/pattern.rb
+++ b/actionpack/lib/action_dispatch/journey/path/pattern.rb
@@ -81,7 +81,7 @@ def accept(node)
           end
 
           def visit_CAT(node)
-            [visit(node.left), visit(node.right)].join
+            "#{visit(node.left)}#{visit(node.right)}"
           end
 
           def visit_SYMBOL(node)