diff --git a/mrbgems/mruby-io/src/file.c b/mrbgems/mruby-io/src/file.c
index cd82cab78..6b364d2fe 100644
--- a/mrbgems/mruby-io/src/file.c
+++ b/mrbgems/mruby-io/src/file.c
@@ -255,7 +255,7 @@ mrb_file_basename(mrb_state *mrb, mrb_value klass)
       path[ridx] = '\0';
       ridx--;
     }
-    if (strncmp(path, "/", 2) == 0) {
+    if (ridx == 0 && path[0] == "/") {
       return mrb_str_new_cstr(mrb, path);
     }
   }
@@ -270,7 +270,7 @@ mrb_file_basename(mrb_state *mrb, mrb_value klass)
   if ((bname = basename(path)) == NULL) {
     mrb_sys_fail(mrb, "basename");
   }
-  if (strncmp(bname, "//", 3) == 0) bname[1] = '\0';  /* patch for Cygwin */
+  if (strcmp(bname, "//") == 0) bname[1] = '\0';  /* patch for Cygwin */
   return mrb_str_new_cstr(mrb, bname);
 #endif
 }