1 files changed, 7 insertions, 0 deletions
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index 288ce3e867..ff33d87901 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -156,6 +156,8 @@ module ActionDispatch
                 next unless URL_OPTIONS.include?(key) && (String === default || Fixnum === default)
                 @defaults[key] ||= default
               end
+            elsif options[:constraints]
+              verify_callable_constraint(options[:constraints])
             end
 
             if Regexp === options[:format]
@@ -165,6 +167,11 @@ module ActionDispatch
             end
           end
 
+          def verify_callable_constraint(callable_constraint)
+            return if callable_constraint.respond_to?(:call) || callable_constraint.respond_to?(:matches?)
+            raise ArgumentError, "Invalid constraint: #{callable_constraint.inspect} must respond to :call or :matches?"
+          end
+
           def normalize_conditions!
             @conditions.merge!(:path_info => path)