diff --git a/.travis.yml b/.travis.yml
index bd2ae443..12b6dd49 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,6 +4,7 @@ php:
   - 7.1
   - 7.2
   - 7.3
+  - 7.4
   - nightly # ignore errors, see below
 
 # lock distro so new future defaults will not break the build
diff --git a/tests/DeferredTest.php b/tests/DeferredTest.php
index 172cb246..423625c3 100644
--- a/tests/DeferredTest.php
+++ b/tests/DeferredTest.php
@@ -37,6 +37,8 @@ public function shouldRejectWithoutCreatingGarbageCyclesIfCancellerRejectsWithEx
     public function shouldRejectWithoutCreatingGarbageCyclesIfParentCancellerRejectsWithException()
     {
         gc_collect_cycles();
+        gc_collect_cycles(); // clear twice to avoid leftovers in PHP 7.4 with ext-xdebug and code coverage turned on
+
         $deferred = new Deferred(function ($resolve, $reject) {
             $reject(new \Exception('foo'));
         });
@@ -50,6 +52,8 @@ public function shouldRejectWithoutCreatingGarbageCyclesIfParentCancellerRejects
     public function shouldRejectWithoutCreatingGarbageCyclesIfCancellerHoldsReferenceAndExplicitlyRejectWithException()
     {
         gc_collect_cycles();
+        gc_collect_cycles(); // clear twice to avoid leftovers in PHP 7.4 with ext-xdebug and code coverage turned on
+
         $deferred = new Deferred(function () use (&$deferred) { });
         $deferred->reject(new \Exception('foo'));
         unset($deferred);