diff --git a/src/range.c b/src/range.c
index 800e646117..5553171b9c 100644
--- a/src/range.c
+++ b/src/range.c
@@ -248,7 +248,7 @@ mrb_range_include(mrb_state *mrb, mrb_value range)
   return mrb_bool_value(include_p);
 }
 
-int
+MRB_API int
 mrb_range_beg_len(mrb_state *mrb, mrb_value range, mrb_int *begp, mrb_int *lenp, mrb_int len, mrb_bool trunc)
 {
   mrb_int beg, end;