diff --git a/iseq.c b/iseq.c
index e5210ca750..f64177dc5b 100644
--- a/iseq.c
+++ b/iseq.c
@@ -493,16 +493,16 @@ rb_iseq_insns_info_encode_positions(const rb_iseq_t *iseq)
 #endif
 }
 
+#if VM_INSN_INFO_TABLE_IMPL == 2
 unsigned int *
 rb_iseq_insns_info_decode_positions(const struct rb_iseq_constant_body *body)
 {
-#if VM_INSN_INFO_TABLE_IMPL == 2
     int size = body->insns_info.size;
     int max_pos = body->iseq_size;
     struct succ_index_table *sd = body->insns_info.succ_index_table;
     return succ_index_table_invert(max_pos, sd, size);
-#endif
 }
+#endif
 
 static VALUE
 finish_iseq_build(rb_iseq_t *iseq)
diff --git a/iseq.h b/iseq.h
index 7c6b56a1d4..eba17168eb 100644
--- a/iseq.h
+++ b/iseq.h
@@ -143,7 +143,9 @@ VALUE iseq_ibf_dump(const rb_iseq_t *iseq, VALUE opt);
 void ibf_load_iseq_complete(rb_iseq_t *iseq);
 const rb_iseq_t *iseq_ibf_load(VALUE str);
 VALUE iseq_ibf_load_extra_data(VALUE str);
+#if VM_INSN_INFO_TABLE_IMPL == 2
 unsigned int *rb_iseq_insns_info_decode_positions(const struct rb_iseq_constant_body *body);
+#endif
 
 RUBY_SYMBOL_EXPORT_BEGIN