diff --git a/iseq.h b/iseq.h
index ee8beb4e9d..9cbfd85cf9 100644
--- a/iseq.h
+++ b/iseq.h
@@ -12,6 +12,11 @@
 #ifndef RUBY_ISEQ_H
 #define RUBY_ISEQ_H 1
 
+#ifndef rb_iseq_t
+typedef struct rb_iseq_struct rb_iseq_t;
+#define rb_iseq_t rb_iseq_t
+#endif
+
 static inline size_t
 rb_call_info_kw_arg_bytes(int keyword_len)
 {
diff --git a/method.h b/method.h
index cb3eda1998..0628559604 100644
--- a/method.h
+++ b/method.h
@@ -118,7 +118,10 @@ typedef enum {
     END_OF_ENUMERATION(VM_METHOD_TYPE)
 } rb_method_type_t;
 
+#ifndef rb_iseq_t
 typedef struct rb_iseq_struct rb_iseq_t;
+#define rb_iseq_t rb_iseq_t
+#endif
 
 typedef struct rb_method_iseq_struct {
     const rb_iseq_t * const iseqptr;              /* should be separated from iseqval */