diff --git a/ChangeLog b/ChangeLog
index 43fc95ba80..72f2be2685 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Aug  2 12:22:22 2010  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* file.c (file_expand_path): wrong condition. [ruby-core:31591]
+
 Mon Aug  2 05:34:48 2010  Tanaka Akira  <akr@fsij.org>
 
 	* ext/pathname/pathname.c (path_realdirpath): Pathname#realdirpath
diff --git a/file.c b/file.c
index f49b46dcbb..712d60ef45 100644
--- a/file.c
+++ b/file.c
@@ -2897,7 +2897,7 @@ file_expand_path(VALUE fname, VALUE dname, int abs_mode, VALUE result)
 	else {
 	    /* specified drive, but not full path */
 	    int same = 0;
-	    if (!NIL_P(dname) || !not_same_drive(dname, s[0])) {
+	    if (!NIL_P(dname) && !not_same_drive(dname, s[0])) {
 		file_expand_path(dname, Qnil, abs_mode, result);
 		BUFINIT();
 		if (has_drive_letter(p) && TOLOWER(p[0]) == TOLOWER(s[0])) {
diff --git a/test/ruby/test_file_exhaustive.rb b/test/ruby/test_file_exhaustive.rb
index 5344494679..4615bceb05 100644
--- a/test/ruby/test_file_exhaustive.rb
+++ b/test/ruby/test_file_exhaustive.rb
@@ -393,6 +393,7 @@ class TestFileExhaustive < Test::Unit::TestCase
       assert_equal(@file, File.expand_path(@file + " "))
       assert_equal(@file, File.expand_path(@file + "."))
       assert_equal(@file, File.expand_path(@file + "::$DATA"))
+      assert_match(/\Ac:\//i, File.expand_path('c:'), '[ruby-core:31591]')
     end
     assert_kind_of(String, File.expand_path("~"))
     assert_raise(ArgumentError) { File.expand_path("~foo_bar_baz_unknown_user_wahaha") }