diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 228b896..4817d70 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -26,6 +26,24 @@ jobs:
       - run: npm ci
       - run: npm test
 
+  compatibility:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby-version: [ "3.3", "3.4" ]
+        rails-version: [ "8.0", "8.1" ]
+    env:
+      RAILS_VERSION: ${{ matrix.rails-version }}
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+      - uses: ruby/setup-ruby@95ef2b042f9d7a56d8268cba8559e2842e2ad01b # v1
+        with:
+          ruby-version: ${{ matrix.ruby-version }}
+          bundler-cache: false
+      - run: bundle lock --update && bundle install --jobs 4
+      - run: bundle exec rake test
+
   postgresql:
     runs-on: ubuntu-latest
     services:
@@ -97,6 +115,7 @@ jobs:
       - mysql
       - static
       - javascript
+      - compatibility
     runs-on: ubuntu-latest
     permissions:
       contents: write
diff --git a/CHANGELOG.md b/CHANGELOG.md
index d882d8d..4e1a95a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,14 @@
 
 ## Unreleased
 
+- Run compatibility CI across the span the gemspec advertises: Ruby 3.3 and 3.4
+  against Rails 8.0 and 8.1. The suite previously ran on one combination, so
+  `>= 8.0` was a claim rather than a tested guarantee. Set `RAILS_VERSION` to
+  pin a Rails line locally.
+- Stop a synchronous lock retry from asking for a negative wait when its
+  deadline expires between the check and the wait, which raised
+  `ArgumentError: time interval must not be negative` instead of the timeout
+  the caller expected. Found by the new compatibility matrix.
 - Add `SolidObjects::WakeUpAdapters::Postgresql`, an optional cross-process
   wake-up using PostgreSQL notifications. In-process signalling cannot reach a
   worker process, so reactive delivery waited out `polling_interval`. With the
diff --git a/Gemfile b/Gemfile
index 80bdaa2..a2b84cc 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,6 +2,16 @@ source "https://rubygems.org"
 
 gemspec
 
+# Compatibility runs pin the Rails line so CI can verify the span the gemspec
+# advertises rather than only the newest release that resolves.
+rails_version = ENV["RAILS_VERSION"]
+if rails_version
+  constraint = "~> #{rails_version}.0"
+  %w[actioncable actionpack actionview activerecord activesupport railties].each do |library|
+    gem library, constraint
+  end
+end
+
 group :development, :test do
   gem "mysql2", ">= 0.5", require: false
   gem "pg", ">= 1.5", require: false
diff --git a/docs/roadmap.md b/docs/roadmap.md
index 4e6bded..7b674f2 100644
--- a/docs/roadmap.md
+++ b/docs/roadmap.md
@@ -36,6 +36,9 @@
   a listening connection per waiting thread and release on supervisor shutdown
 - Inline RBS generation/validation, Steep, Standard Ruby, Solid Queue's exact
   RuboCop policy, and a warning-free Brakeman scan
+- Compatibility CI across the supported span: Ruby 3.3 and 3.4 against Rails 8.0
+  and 8.1, pinned through `RAILS_VERSION` so the advertised range is verified
+  rather than assumed
 - A JavaScript suite covering the state payload and batched refresh browser
   modules, run in CI with Node's test runner and jsdom, with every GitHub
   Actions reference pinned to a commit SHA
diff --git a/lib/solid_objects/database_adapters/sqlite.rb b/lib/solid_objects/database_adapters/sqlite.rb
index b885252..fb84927 100644
--- a/lib/solid_objects/database_adapters/sqlite.rb
+++ b/lib/solid_objects/database_adapters/sqlite.rb
@@ -160,13 +160,15 @@ def wait_before_busy_retry(attempts)
         end
       end
 
+      # The deadline can expire between the check above and this wait, which
+      # would otherwise ask for a negative interval.
       # @rbs () -> void
       def wait_before_retry
+        interval = [ LOCK_RETRY_INTERVAL, SyncDeadline.remaining ].min
+        return unless interval.positive?
+
         LOCK_RETRY_MUTEX.synchronize do
-          LOCK_RETRY_CONDITION.wait(
-            LOCK_RETRY_MUTEX,
-            [ LOCK_RETRY_INTERVAL, SyncDeadline.remaining ].min
-          )
+          LOCK_RETRY_CONDITION.wait(LOCK_RETRY_MUTEX, interval)
         end
       end
     end
diff --git a/sig/generated/lib/solid_objects/database_adapters/sqlite.rbs b/sig/generated/lib/solid_objects/database_adapters/sqlite.rbs
index ca182a3..61e3d49 100644
--- a/sig/generated/lib/solid_objects/database_adapters/sqlite.rbs
+++ b/sig/generated/lib/solid_objects/database_adapters/sqlite.rbs
@@ -52,6 +52,8 @@ module SolidObjects
       # @rbs (Integer) -> void
       def wait_before_busy_retry: (Integer) -> void
 
+      # The deadline can expire between the check above and this wait, which
+      # would otherwise ask for a negative interval.
       # @rbs () -> void
       def wait_before_retry: () -> void
     end
diff --git a/test/integration/synchronous_invocation_test.rb b/test/integration/synchronous_invocation_test.rb
index ec10994..59259ca 100644
--- a/test/integration/synchronous_invocation_test.rb
+++ b/test/integration/synchronous_invocation_test.rb
@@ -552,6 +552,15 @@ def wait(timeout:)
       "a synchronous call should read the clock once per transaction, not once per step"
   end
 
+  test "a retry wait whose deadline already expired does not raise" do
+    skip unless SolidObjects::Record.connection.adapter_name.match?(/sqlite/i)
+    adapter = SolidObjects.database_adapter
+
+    SolidObjects::SyncDeadline.with(timeout: -1) do
+      assert_nothing_raised { adapter.send(:wait_before_retry) }
+    end
+  end
+
   test "sync discovers the configured SQLite busy wait it has to restore" do
     skip unless SolidObjects::Record.connection.adapter_name.match?(/sqlite/i)