1 files changed, 1 insertions, 1 deletions
diff --git a/vm_core.h b/vm_core.h
index c5417d9381..e302e62a4b 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -435,7 +435,7 @@ typedef struct rb_thread_struct {
     struct rb_unblock_callback unblock;
     VALUE locking_mutex;
     struct rb_mutex_struct *keeping_mutexes;
-    int transition_for_lock;
+    volatile int transition_for_lock;
 
     struct rb_vm_tag *tag;
     struct rb_vm_protect_tag *protect_tag;