diff --git a/actionpack/lib/action_dispatch/journey/formatter.rb b/actionpack/lib/action_dispatch/journey/formatter.rb
index 545b67422d5a7ba95ebafbe799f8c764a3a2bb9a..985cf8b9470eb4568c6893aead8deb2d4bad8970 100644
--- a/actionpack/lib/action_dispatch/journey/formatter.rb
+++ b/actionpack/lib/action_dispatch/journey/formatter.rb
@@ -111,15 +111,27 @@ def non_recursive(cache, options)
           routes
         end
 
+        module RegexCaseComparator
+          DEFAULT_INPUT = /[-_.a-zA-Z0-9]+\/[-_.a-zA-Z0-9]+/
+          DEFAULT_REGEX = /\A#{DEFAULT_INPUT}\Z/
+
+          def self.===(regex)
+            DEFAULT_INPUT == regex
+          end
+        end
+
         # Returns an array populated with missing keys if any are present.
         def missing_keys(route, parts)
           missing_keys = []
           tests = route.path.requirements
           route.required_parts.each { |key|
-            if tests.key?(key)
-              missing_keys << key unless /\A#{tests[key]}\Z/ === parts[key]
-            else
+            case tests[key]
+            when nil
               missing_keys << key unless parts[key]
+            when RegexCaseComparator
+              missing_keys << key unless RegexCaseComparator::DEFAULT_REGEX === parts[key]
+            else
+              missing_keys << key unless /\A#{tests[key]}\Z/ === parts[key]
             end
           }
           missing_keys