1 files changed, 1 insertions, 1 deletions
diff --git a/src/string.c b/src/string.c
index 61aa08577..15fcc502a 100644
--- a/src/string.c
+++ b/src/string.c
@@ -576,7 +576,7 @@ str_rindex(mrb_state *mrb, mrb_value str, mrb_value sub, mrb_int pos)
   }
 }
 
-mrb_int
+MRB_API mrb_int
 mrb_str_strlen(mrb_state *mrb, struct RString *s)
 {
   mrb_int i, max = RSTR_LEN(s);