diff --git a/mrbgems/mruby-io/src/file.c b/mrbgems/mruby-io/src/file.c
index 6210915ec2..97990b37ae 100644
--- a/mrbgems/mruby-io/src/file.c
+++ b/mrbgems/mruby-io/src/file.c
@@ -241,85 +241,58 @@ mrb_file_dirname(mrb_state *mrb, mrb_value klass)
 static mrb_value
 mrb_file_basename(mrb_state *mrb, mrb_value klass)
 {
-#if defined(_WIN32)
-  char bname[_MAX_DIR];
-  char extname[_MAX_EXT];
-  char *path;
-  const char *suffix = NULL;
-
-  mrb_get_args(mrb, "z|z", &path, &suffix);
-  size_t ridx = strlen(path);
-  if (ridx > 0) {
-    ridx--;
-    while (ridx > 0 && (path[ridx] == '/' || path[ridx] == '\\')) {
-      path[ridx] = '\0';
-      ridx--;
-    }
-    if (ridx == 0 && path[0] == '/') {
-      mrb_value result = mrb_str_new_cstr(mrb, path);
-      if (suffix && *suffix) {
-        mrb_int blen = RSTRING_LEN(result);
-        mrb_int slen = strlen(suffix);
-        if (blen > slen && memcmp(RSTRING_PTR(result) + blen - slen, suffix, slen) == 0) {
-          mrb_str_resize(mrb, result, blen - slen);
-        }
-      }
-      return result;
-    }
-  }
-  _splitpath((const char*)path, NULL, NULL, bname, extname);
-  mrb_value buffer = mrb_str_new_cstr(mrb, bname);
-  mrb_str_cat_cstr(mrb, buffer, extname);
-  if (suffix && *suffix) {
-    mrb_int blen = RSTRING_LEN(buffer);
-    mrb_int slen = strlen(suffix);
-    if (blen > slen && memcmp(RSTRING_PTR(buffer) + blen - slen, suffix, slen) == 0) {
-      mrb_str_resize(mrb, buffer, blen - slen);
-    }
-  }
-  return buffer;
-#else
-  char *path;
+  const char *path;
   const char *suffix = NULL;
 
   mrb_get_args(mrb, "z|z", &path, &suffix);
 
-  // Copy path to a local buffer to avoid modifying the original string
-  size_t len = strlen(path);
-  if (len == 0) {
+  const char *endp = path + strlen(path);
+  if (path == endp) {
     return mrb_str_new_lit(mrb, ".");
   }
 
+#ifdef _WIN32
+  if (UNC_PATH_P(path)) {
+    path += 2;
+    SKIP_DIRSEP(path);
+    NEXT_DIRSEP(path); // skip server name
+    SKIP_DIRSEP(path);
+    NEXT_DIRSEP(path); // skip share name
+  }
+  else if (DRIVE_LETTER_P(path)) {
+    path += 2;
+    if (path == endp) {
+      return mrb_str_new_lit(mrb, "");
+    }
+  }
+#endif // _WIN32
+
   // Remove trailing slashes (except when path is only "/")
-  while (len > 1 && path[len - 1] == '/') {
-    len--;
+  while (path < endp && DIRSEP_P(endp[-1])) {
+    endp--;
   }
 
   // Find the last path separator
-  ssize_t base = len - 1;
-  while (base >= 0 && path[base] != '/') {
+  const char *base = endp;
+  while (path < base && !DIRSEP_P(base[-1])) {
     base--;
   }
-  base++; // move to the first character after '/'
 
   // If path is all slashes, return "/"
-  if ((size_t)base == len) {
+  if (base == endp) {
     return mrb_str_new_lit(mrb, "/");
   }
 
-  mrb_value result = mrb_str_new(mrb, path + base, len - base);
-
   // Suffix removal (CRuby compatible)
   if (suffix && *suffix) {
-    mrb_int blen = RSTRING_LEN(result);
+    mrb_int blen = endp - base;
     mrb_int slen = strlen(suffix);
-    if (blen > slen && memcmp(RSTRING_PTR(result) + blen - slen, suffix, slen) == 0) {
-      mrb_str_resize(mrb, result, blen - slen);
+    if (blen > slen && memcmp(endp - slen, suffix, slen) == 0) {
+      endp -= slen;
     }
   }
 
-  return result;
-#endif
+  return mrb_str_new(mrb, base, endp - base);
 }
 
 static mrb_value
diff --git a/mrbgems/mruby-io/test/file.rb b/mrbgems/mruby-io/test/file.rb
index e6eda54340..fb5f16f5bd 100644
--- a/mrbgems/mruby-io/test/file.rb
+++ b/mrbgems/mruby-io/test/file.rb
@@ -57,6 +57,40 @@ def assert_dirname_with_level(path, results)
   assert_equal 'foo.rb', File.basename('foo.rb', '.RB') # case-sensitive
 end
 
+if MRubyIOTestUtil.win?
+  assert('File.basename (for Windows)') do
+    assert_equal '/',  File.basename('/')
+    assert_equal '/',  File.basename('//a')
+    assert_equal '/',  File.basename('//a/')
+    assert_equal '/',  File.basename('//a/b')
+    assert_equal '/',  File.basename('//a/b/')
+    assert_equal 'c',  File.basename('//a/b/c')
+    assert_equal 'c',  File.basename('//a/b/c/')
+    assert_equal '/',  File.basename("\\\\a\\b")
+    assert_equal '',   File.basename('c:')
+    assert_equal '/',  File.basename('c:/')
+    assert_equal 'a',  File.basename('c:/a')
+    assert_equal 'a',  File.basename('c:/a/')
+    assert_equal 'b',  File.basename('c:/a/b')
+    assert_equal '/',  File.basename("c:\\")
+  end
+else
+  assert('File.basename (for generic)') do
+    assert_equal '/',  File.basename('/')
+    assert_equal 'a',  File.basename('//a')
+    assert_equal 'a',  File.basename('//a/')
+    assert_equal 'b',  File.basename('//a/b')
+    assert_equal 'b',  File.basename('//a/b/')
+    assert_equal 'c',  File.basename('//a/b/c')
+    assert_equal 'c',  File.basename('//a/b/c/')
+    assert_equal 'c:', File.basename('c:')
+    assert_equal 'c:', File.basename('c:/')
+    assert_equal 'a',  File.basename('c:/a')
+    assert_equal 'a',  File.basename('c:/a/')
+    assert_equal 'b',  File.basename('c:/a/b')
+  end
+end
+
 assert('File.dirname') do
   assert_equal '.',    File.dirname('')
   assert_equal '.',    File.dirname('a')