diff --git a/test/resource_test.rb b/test/resource_test.rb
index 9e895b33..deaac470 100644
--- a/test/resource_test.rb
+++ b/test/resource_test.rb
@@ -173,7 +173,7 @@ def test_acquire_timeout
 
   def test_acquire_and_release_timeout
     resource = create_resource(:testing, tickets: 1, timeout: 1)
-    start_time = Time.now.to_f
+    start_time = Process.clock_gettime(Process::CLOCK_MONOTONIC)
 
     # Grab the only ticket
     resource.acquire_semaphore
@@ -182,12 +182,13 @@ def test_acquire_and_release_timeout
     assert_raises(Semian::TimeoutError) do
       resource.acquire_semaphore
     end
+    end_time = Process.clock_gettime(Process::CLOCK_MONOTONIC)
 
     # Should work now
     resource.release_semaphore
 
     # Ensure we actually waited for the timeout
-    assert_in_delta(1, Time.now.to_f - start_time, EPSILON)
+    assert_in_delta(1, end_time - start_time, EPSILON)
   end
 
   def test_release_semaphore_without_acquire