diff --git a/cross_language_tests/challenge.rb b/cross_language_tests/challenge.rb
index bc6827d..5745f4a 100644
--- a/cross_language_tests/challenge.rb
+++ b/cross_language_tests/challenge.rb
@@ -20,7 +20,7 @@
 when "generate"
   # write the private encryption key to the test directory to retrieve in later tests
   key = OpenSSL::PKey::EC.new(test_case["RubyPrivateSigningKey"])
-  result = Krypto::Challenge.generate(key, test_case["ChallengeId"], test_case["ChallengeData"], test_case["RequestData"], timestamp: Time.now)
+  result = Krypto::Challenge.generate(key, test_case["ChallengeId"], test_case["ChallengeData"], test_case["RequestData"], Time.now)
   File.write(private_encryption_key_path, Base64.strict_encode64(result[1]))
 
   # return the challenge
diff --git a/lib/krypto/challenge.rb b/lib/krypto/challenge.rb
index 35a0136..26e6eb4 100644
--- a/lib/krypto/challenge.rb
+++ b/lib/krypto/challenge.rb
@@ -6,7 +6,7 @@
 
 module Krypto
   class Challenge
-    def self.generate(signing_key, challenge_id, challenge_data, request_data, timestamp: Time.now)
+    def self.generate(signing_key, challenge_id, challenge_data, request_data, timestamp = Time.now)
       private_encryption_key = RbNaCl::PrivateKey.generate
       public_encryption_key = private_encryption_key.public_key