diff --git a/gc.c b/gc.c
index c03738986c..3dc63433a7 100644
--- a/gc.c
+++ b/gc.c
@@ -6875,6 +6875,7 @@ each_machine_stack_value(const rb_execution_context_t *ec, void (*cb)(rb_objspac
     VALUE *stack_start, *stack_end;
 
     GET_STACK_BOUNDS(stack_start, stack_end, 0);
+    RUBY_DEBUG_LOG("ec->th:%u stack_start:%p stack_end:%p", rb_ec_thread_ptr(ec)->serial, stack_start, stack_end);
     each_stack_location(objspace, ec, stack_start, stack_end, cb);
 }