diff --git a/lib/sidekiq_unique_jobs/timeout/calculator.rb b/lib/sidekiq_unique_jobs/timeout/calculator.rb
index 1d73ee547..0b640a79c 100644
--- a/lib/sidekiq_unique_jobs/timeout/calculator.rb
+++ b/lib/sidekiq_unique_jobs/timeout/calculator.rb
@@ -39,7 +39,7 @@ def lock_expiration
         @lock_expiration ||= begin
           expiration = item[LOCK_EXPIRATION_KEY]
           expiration ||= worker_options[LOCK_EXPIRATION_KEY]
-          expiration && expiration + time_until_scheduled
+          expiration && expiration.to_i + time_until_scheduled
         end
       end