1 files changed, 4 insertions, 0 deletions
diff --git a/thread.c b/thread.c
index 492722b085..6c4e6506e8 100644
--- a/thread.c
+++ b/thread.c
@@ -596,7 +596,11 @@ thread_cleanup_func_before_exec(void *th_ptr)
 {
     rb_thread_t *th = th_ptr;
     th->status = THREAD_KILLED;
+    // The thread stack doesn't exist in the forked process:
     th->ec->machine.stack_start = th->ec->machine.stack_end = NULL;
+    
+    // The vm_stack is `alloca`ed on the thread stack, so it's gone too:
+    rb_ec_clear_vm_stack(th->ec);
 }
 
 static void