diff --git a/src/amber/router/routed_result.cr b/src/amber/router/routed_result.cr
index 88be2dd..6fe0540 100644
--- a/src/amber/router/routed_result.cr
+++ b/src/amber/router/routed_result.cr
@@ -5,7 +5,13 @@ module Amber::Router
     def initialize(@terminal_segment : TerminalSegment(T)?)
     end
 
-    delegate :[], :[]=, to: @params
+    # This doesn't work, bug in crystal 0.25:
+    # delegate :[], :[]=, to: @params
+    delegate :[], to: @params
+
+    def []=(k : String, v : String) : String
+      @params[k.to_s] = v
+    end
 
     def terminal_segment
       @terminal_segment.not_nil!