diff --git a/ext/mbstring/libmbfl/mbfl/mbfl_encoding.c b/ext/mbstring/libmbfl/mbfl/mbfl_encoding.c
index d8049617014..be861629d0e 100644
--- a/ext/mbstring/libmbfl/mbfl/mbfl_encoding.c
+++ b/ext/mbstring/libmbfl/mbfl/mbfl_encoding.c
@@ -114,22 +114,8 @@
 #endif
 
 
-static const char *mbfl_encoding_auto_aliases[] = {"unknown", NULL};
-
-static const mbfl_encoding mbfl_encoding_auto = {
-	mbfl_no_encoding_auto,
-	"auto",
-	NULL,
-	(const char *(*)[])&mbfl_encoding_auto_aliases,
-	NULL,
-	0,
-	NULL,
-	NULL
-};
-
 static const mbfl_encoding *mbfl_encoding_ptr_list[] = {
 	&mbfl_encoding_pass,
-	&mbfl_encoding_auto,
 	&mbfl_encoding_wchar,
 	&mbfl_encoding_byte2be,
 	&mbfl_encoding_byte2le,
diff --git a/ext/mbstring/libmbfl/mbfl/mbfl_encoding.h b/ext/mbstring/libmbfl/mbfl/mbfl_encoding.h
index 2952977fd88..c3a9c0affc7 100644
--- a/ext/mbstring/libmbfl/mbfl/mbfl_encoding.h
+++ b/ext/mbstring/libmbfl/mbfl/mbfl_encoding.h
@@ -36,7 +36,6 @@
 enum mbfl_no_encoding {
 	mbfl_no_encoding_invalid = -1,
 	mbfl_no_encoding_pass,
-	mbfl_no_encoding_auto,
 	mbfl_no_encoding_wchar,
 	mbfl_no_encoding_byte2be,
 	mbfl_no_encoding_byte2le,
diff --git a/ext/mbstring/tests/mb_preferred_mime_name.phpt b/ext/mbstring/tests/mb_preferred_mime_name.phpt
index 1fa73421f69..df05027c3c6 100644
--- a/ext/mbstring/tests/mb_preferred_mime_name.phpt
+++ b/ext/mbstring/tests/mb_preferred_mime_name.phpt
@@ -38,7 +38,7 @@ echo "== INVALID PARAMETER ==\n";
 var_dump(mb_preferred_mime_name('BAD_NAME'));
 
 // No preferred name
-var_dump(mb_preferred_mime_name('auto'));
+var_dump(mb_preferred_mime_name('pass'));
 ?>
 --EXPECTF--
 Shift_JIS
@@ -55,5 +55,5 @@ UCS-4
 Warning: mb_preferred_mime_name(): Unknown encoding "BAD_NAME" in %s on line %d
 bool(false)
 
-Warning: mb_preferred_mime_name(): No MIME preferred name corresponding to "auto" in %s on line %d
+Warning: mb_preferred_mime_name(): No MIME preferred name corresponding to "pass" in %s on line %d
 bool(false)