--- old/src/share/vm/gc/shenandoah/shenandoahHeapRegion.cpp	2017-03-24 18:44:29.958388604 +0100
+++ new/src/share/vm/gc/shenandoah/shenandoahHeapRegion.cpp	2017-03-24 18:44:29.902388756 +0100
@@ -291,7 +291,10 @@
   _heap->set_complete_top_at_mark_start(bottom(), bottom());
   // We can only safely reset the C-TAMS pointer if the bitmap is clear for that region.
   assert(_heap->is_complete_bitmap_clear_range(bottom(), end()), "must be clear");
-  _heap->connection_matrix()->clear_region(region_number());
+
+  if (UseShenandoahMatrix) {
+    _heap->connection_matrix()->clear_region(region_number());
+  }
 }
 
 HeapWord* ShenandoahHeapRegion::block_start_const(const void* p) const {