diff --git a/lib/celluloid/stack_dump.rb b/lib/celluloid/stack_dump.rb
index <HASH>..<HASH> 100644
--- a/lib/celluloid/stack_dump.rb
+++ b/lib/celluloid/stack_dump.rb
@@ -45,7 +45,7 @@ module Celluloid
         state.tasks = tasks.collect { |t| TaskState.new(t.class, t.status) }
       end
 
-      state.backtrace = actor.thread.backtrace
+      state.backtrace = actor.thread.backtrace if actor.thread
       state
     end
only dump actor backtrace if available

On JRuby actor.thread is nil for some reason?