diff -r a8db7fd22fd1 -r 40dc805f4709 src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp
--- a/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp	Mon Apr 08 12:19:51 2019 -0400
+++ b/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp	Mon Apr 08 18:42:27 2019 +0200
@@ -1204,7 +1204,9 @@
 
 void ShenandoahHeap::gc_threads_do(ThreadClosure* tcl) const {
   workers()->threads_do(tcl);
-  _safepoint_workers->threads_do(tcl);
+  if (_safepoint_workers != NULL) {
+    _safepoint_workers->threads_do(tcl);
+  }
   if (ShenandoahStringDedup::is_enabled()) {
     ShenandoahStringDedup::threads_do(tcl);
   }