diff --git a/include/mruby.h b/include/mruby.h
index 769f9734c..59188e6b5 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -277,8 +277,8 @@ typedef struct mrb_state {
 #endif
 
 #ifdef MRB_ENABLE_DEBUG_HOOK
-  void (*code_fetch_hook)(struct mrb_state* mrb, struct mrb_irep *irep, const mrb_code *pc, mrb_value *regs);
-  void (*debug_op_hook)(struct mrb_state* mrb, struct mrb_irep *irep, const mrb_code *pc, mrb_value *regs);
+  void (*code_fetch_hook)(struct mrb_state* mrb, const struct mrb_irep *irep, const mrb_code *pc, mrb_value *regs);
+  void (*debug_op_hook)(struct mrb_state* mrb, const struct mrb_irep *irep, const mrb_code *pc, mrb_value *regs);
 #endif
 
 #ifdef MRB_BYTECODE_DECODE_OPTION
diff --git a/mrbgems/mruby-bin-debugger/tools/mrdb/mrdb.c b/mrbgems/mruby-bin-debugger/tools/mrdb/mrdb.c
index 8fab3c2e8..0ca3bc5eb 100644
--- a/mrbgems/mruby-bin-debugger/tools/mrdb/mrdb.c
+++ b/mrbgems/mruby-bin-debugger/tools/mrdb/mrdb.c
@@ -545,7 +545,7 @@ check_method_breakpoint(mrb_state *mrb, mrb_irep *irep, const mrb_code *pc, mrb_
 }
 
 static void
-mrb_code_fetch_hook(mrb_state *mrb, mrb_irep *irep, const mrb_code *pc, mrb_value *regs)
+mrb_code_fetch_hook(mrb_state *mrb, const mrb_irep *irep, const mrb_code *pc, mrb_value *regs)
 {
   const char *file;
   int32_t line;