1 files changed, 1 insertions, 0 deletions
diff --git a/vm_core.h b/vm_core.h
index 51b51255b3..5fa11487f7 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -539,6 +539,7 @@ typedef struct rb_vm_struct {
     struct rb_thread_struct *main_thread;
     struct rb_thread_struct *running_thread;
 
+    rb_serial_t fork_gen;
     struct list_head waiting_fds; /* <=> struct waiting_fd */
     struct list_head living_threads;
     VALUE thgroup_default;