foo.diff

diff --git a/rayon-core/src/registry.rs b/rayon-core/src/registry.rs
index 63d8a31..ced0b9c 100644
--- a/rayon-core/src/registry.rs
+++ b/rayon-core/src/registry.rs
@@ -589,6 +589,13 @@ impl WorkerThread {
         });
     }
 
+    unsafe fn unset_current() {
+        WORKER_THREAD_STATE.with(|t| {
+            assert!(!t.get().is_null());
+            t.set(std::ptr::null());
+        });
+    }
+
     /// Returns the registry that owns this worker thread.
     pub fn registry(&self) -> &Arc<Registry> {
         &self.registry
@@ -789,6 +796,7 @@ unsafe fn main_loop(
         }
         // We're already exiting the thread, there's nothing else to do.
     }
+    WorkerThread::unset_current();
 }
 
 /// If already in a worker-thread, just execute `op`.  Otherwise,