diff --git a/ChangeLog b/ChangeLog
index 6453530f3c..8908744cd4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Mar 16 11:23:42 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* file.c (file_expand_path): ignore dname if it has different
+	  drive letter or UNC.
+
 Tue Mar 16 07:16:56 2010  Tanaka Akira  <akr@fsij.org>
 
 	* tool/transcode-tblgen.rb: redundant loop removed.
diff --git a/file.c b/file.c
index b6205cf899..64fe824ec2 100644
--- a/file.c
+++ b/file.c
@@ -2518,6 +2518,12 @@ static const char file_alt_separator[] = {FILE_ALT_SEPARATOR, '\0'};
 # define CharNext(p) ((p) + 1)
 #endif
 
+#if defined(DOSISH_UNC)
+#define has_unc(buf) (isdirsep((buf)[0]) && isdirsep((buf)[1]))
+#else
+#define has_unc(buf) 0
+#endif
+
 #ifdef DOSISH_DRIVE_LETTER
 static inline int
 has_drive_letter(const char *buf)
@@ -2556,6 +2562,19 @@ getcwdofdrv(int drv)
     }
     return drvcwd;
 }
+
+static inline int
+not_same_drive(VALUE path, int drive)
+{
+    const char *p = RSTRING_PTR(path);
+    if (RSTRING_LEN(path) < 2) return 0;
+    if (has_drive_letter(p)) {
+	return TOLOWER(p[0]) != TOLOWER(drive);
+    }
+    else {
+	return has_unc(p);
+    }
+}
 #endif
 
 static inline char *
@@ -2781,7 +2800,7 @@ 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)) {
+	    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])) {