--- old/src/hotspot/share/gc/shared/cardTableBarrierSet.cpp	2019-02-25 16:56:59.747142017 -0500
+++ new/src/hotspot/share/gc/shared/cardTableBarrierSet.cpp	2019-02-25 16:56:59.331120083 -0500
@@ -194,11 +194,13 @@
 #endif
 }
 
-void CardTableBarrierSet::on_thread_detach(JavaThread* thread) {
+void CardTableBarrierSet::on_thread_detach(Thread* thread) {
   // The deferred store barriers must all have been flushed to the
   // card-table (or other remembered set structure) before GC starts
   // processing the card-table (or other remembered set).
-  flush_deferred_card_mark_barrier(thread);
+  if (thread->is_Java_thread()) { // Only relevant for Java threads.
+    flush_deferred_card_mark_barrier((JavaThread*)thread);
+  }
 }
 
 bool CardTableBarrierSet::card_mark_must_follow_store() const {