--- old/test/jdk/jdk/jfr/event/gc/collection/TestG1ParallelPhases.java	2019-11-11 14:26:31.281212784 +0100
+++ new/test/jdk/jdk/jfr/event/gc/collection/TestG1ParallelPhases.java	2019-11-11 14:26:31.077211585 +0100
@@ -176,6 +176,9 @@
     public static void provokeMixedGC(int g1HeapRegionSize) {
         final var arraySize = 20_000;
         var liveOldObjects = new ArrayList<byte[]>();
+
+        // Make sure the heap is in a known state.
+        getWhiteBox().fullGC();
         allocateOldObjects(liveOldObjects, g1HeapRegionSize, arraySize);
         waitTillCMCFinished(10);
         getWhiteBox().g1StartConcMarkCycle();