diff --git a/ChangeLog b/ChangeLog
index dc04f84ea0..619bdebee5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Nov 18 18:07:05 2005  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* file.c (rb_file_s_dirname): should use skipprefix for UNC path.
+	  pointed out by nobu ([ruby-dev:27744]). fixed: [ruby-core:5076]
+
 Fri Nov 18 17:35:09 2005  Hidetoshi NAGAI  <nagai@ai.kyutech.ac.jp>
 
 	* ext/tk/lib/multi-tk.rb: add restriction to access the entried
@@ -16,7 +21,7 @@ Fri Nov 18 17:35:09 2005  Hidetoshi NAGAI  <nagai@ai.kyutech.ac.jp>
 
 Fri Nov 18 16:47:33 2005  NAKAMURA Usaku  <usa@ruby-lang.org>
 
-	* file.c (file_s_dirname): added checks for some patterns with drive
+	* file.c (rb_file_s_dirname): added checks for some patterns with drive
 	  letter. fixed: [ruby-dev:27738]
 
 	* test/ruby/test_path.rb (test_dirname): added tests for above
diff --git a/file.c b/file.c
index 669929b606..e427cedade 100644
--- a/file.c
+++ b/file.c
@@ -2626,8 +2626,8 @@ rb_file_s_dirname(VALUE klass, VALUE fname)
     name = StringValueCStr(fname);
     root = skiproot(name);
 #ifdef DOSISH_UNC
-    if (root > name + 2 && isdirsep(*name))
-	name = root - 2;
+    if (root > name + 1 && isdirsep(*name))
+	root = skipprefix(name = root - 2);
 #else
     if (root > name + 1)
 	name = root - 1;
diff --git a/test/ruby/test_path.rb b/test/ruby/test_path.rb
index 4b9365508a..09ab4ac677 100644
--- a/test/ruby/test_path.rb
+++ b/test/ruby/test_path.rb
@@ -95,23 +95,31 @@ class TestPath < Test::Unit::TestCase
     if /(bcc|ms|cyg)win|mingw|djgpp|human|emx/ =~ RUBY_PLATFORM
       # DOSISH_UNC
       assert_equal('//', File.dirname('//'))
-      assert_equal('//', File.dirname('//a'))
-      assert_equal('//', File.dirname('//a/'))
-      assert_equal('//a', File.dirname('//a/b'))
+      assert_equal('//a', File.dirname('//a'))
+      assert_equal('//a/', File.dirname('//a/'))
+      assert_equal('//a/b', File.dirname('//a/b'))
+      assert_equal('//a/b', File.dirname('//a/b/'))
+      assert_equal('//a/b', File.dirname('//a/b/c'))
       assert_equal('//', File.dirname('///'))
-      assert_equal('//', File.dirname('///a'))
-      assert_equal('//', File.dirname('///a/'))
-      assert_equal('//a', File.dirname('///a/b'))
+      assert_equal('//a', File.dirname('///a'))
+      assert_equal('//a/', File.dirname('///a/'))
+      assert_equal('//a/b', File.dirname('///a/b'))
+      assert_equal('//a/b', File.dirname('///a/b/'))
+      assert_equal('//a/b', File.dirname('///a/b/c'))
     else
       # others
       assert_equal('/', File.dirname('//'))
       assert_equal('/', File.dirname('//a'))
       assert_equal('/', File.dirname('//a/'))
       assert_equal('/a', File.dirname('//a/b'))
+      assert_equal('/a', File.dirname('//a/b/'))
+      assert_equal('/a/b', File.dirname('//a/b/c'))
       assert_equal('/', File.dirname('///'))
       assert_equal('/', File.dirname('///a'))
       assert_equal('/', File.dirname('///a/'))
       assert_equal('/a', File.dirname('///a/b'))
+      assert_equal('/a', File.dirname('///a/b/'))
+      assert_equal('/a/b', File.dirname('///a/b/c'))
     end
   end
 end