From 4687f8790c64b6ebfad179b41e30a02c2a4800ba Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Sat, 7 Mar 2020 14:58:05 +0900
Subject: Merge the update suggested by @mattn; ref #4950

---
 mrbgems/mruby-io/src/file.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mrbgems/mruby-io/src/file.c b/mrbgems/mruby-io/src/file.c
index dafcac533..b94649534 100644
--- a/mrbgems/mruby-io/src/file.c
+++ b/mrbgems/mruby-io/src/file.c
@@ -283,8 +283,10 @@ static int
 mrb_file_is_absolute_path(const char *path)
 {
 #ifdef _WIN32
-  if (strlen(path) < 2) return 0;
-  return path[0] >= 64 && path[0] <= 90 && path[1] == ':'; // 64 to 90 is ASCII
+#define IS_PATHSEP(x) (x == '/' || x == '\')
+  if (strlen(path) < 3) return 0;
+  return (isalpha(path[0]) && path[1] == ':' && IS_PATHSEP(path[2]));
+#undef IS_PATHSEP
 #else
   return (path[0] == '/');
 #endif
-- 
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