diff --git a/mrbgems/mruby-fiber/src/fiber.c b/mrbgems/mruby-fiber/src/fiber.c
index 7e1ea1a78..baddf65ce 100644
--- a/mrbgems/mruby-fiber/src/fiber.c
+++ b/mrbgems/mruby-fiber/src/fiber.c
@@ -391,21 +391,18 @@ fiber_to_s(mrb_state *mrb, mrb_value self)
     mrb_str_cat_lit(mrb, s, ":");
   }
   mrb_str_cat_str(mrb, s, mrb_ptr_to_str(mrb, mrb_ptr(self)));
-  mrb_str_cat_lit(mrb, s, " ");
 
   const char *file;
   int32_t line;
   const struct RProc *p = f->cxt->cibase->proc;
   if (f->cxt->status != MRB_FIBER_TERMINATED && !MRB_PROC_CFUNC_P(p) && !MRB_PROC_ALIAS_P(p) &&
       mrb_debug_get_position(mrb, p->body.irep, 0, &line, &file)) {
+    mrb_str_cat_lit(mrb, s, " ");
     mrb_str_cat_cstr(mrb, s, file);
     mrb_str_cat_lit(mrb, s, ":");
     char buf[16];
     mrb_str_cat_cstr(mrb, s, mrb_int_to_cstr(buf, sizeof(buf), line, 10));
   }
-  else {
-    mrb_str_cat_lit(mrb, s, "(unknown):0");
-  }
 
   const char *st;
   switch (fiber_ptr(self)->cxt->status) {