diff --git a/spec/models/event_registration_spec.rb b/spec/models/event_registration_spec.rb
index 8a37cc56f5..ec364e1cd8 100644
--- a/spec/models/event_registration_spec.rb
+++ b/spec/models/event_registration_spec.rb
@@ -535,6 +535,10 @@ def registration_with_scholarship
   end
 
   describe "#joinable?" do
+    # Freeze the clock so the join-window boundary cases (events placed exactly
+    # 1 minute inside the 30-minute buffer) can't flake on wall-clock drift.
+    before { freeze_time }
+
     let(:event) { create(:event, cost_cents: 1099, start_date: 1.hour.ago, end_date: 1.hour.from_now) }
     let(:user) { create(:user, :with_person) }
 
diff --git a/spec/rails_helper.rb b/spec/rails_helper.rb
index 3c5a4e6834..962224f3db 100644
--- a/spec/rails_helper.rb
+++ b/spec/rails_helper.rb
@@ -48,6 +48,10 @@
 RSpec.configure do |config|
   # Gives travel method for time helpers
   config.include ActiveSupport::Testing::TimeHelpers
+  # RSpec doesn't run minitest teardown, so travel_to never auto-reverts — freeze
+  # one example and the frozen clock leaks into later specs. Always reset after
+  # each example (no-op when time wasn't traveled).
+  config.after { travel_back }
 
   # Include pagination helper globally
   config.include PaginationHelpers