diff --git a/vm_core.h b/vm_core.h
index bcb0aae7ce..83e67dc43c 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -1334,7 +1334,7 @@ static inline const rb_iseq_t *
 vm_block_iseq(const struct rb_block *block)
 {
     switch (vm_block_type(block)) {
-      case block_type_iseq: return block->as.captured.code.iseq;
+      case block_type_iseq: return rb_iseq_check(block->as.captured.code.iseq);
       case block_type_proc: return vm_proc_iseq(block->as.proc);
       case block_type_ifunc:
       case block_type_symbol: return NULL;
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index a1c3a9809d..903e6c4ab5 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -2562,7 +2562,7 @@ vm_invoke_iseq_block(rb_thread_t *th, rb_control_frame_t *reg_cfp,
 		     struct rb_calling_info *calling, const struct rb_call_info *ci,
 		     int is_lambda, const struct rb_captured_block *captured)
 {
-    const rb_iseq_t *iseq = captured->code.iseq;
+    const rb_iseq_t *iseq = rb_iseq_check(captured->code.iseq);
     const int arg_size = iseq->body->param.size;
     VALUE * const rsp = GET_SP() - calling->argc;
     int opt_pc = vm_callee_setup_block_arg(th, calling, ci, iseq, rsp, is_lambda ? arg_setup_lambda : arg_setup_block);