diff --git a/ChangeLog b/ChangeLog
index 5927aab34c..3bcf5d179c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Nov 22 23:52:06 2005  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/optparse.rb: match incomplete (in current enconding) multibyte
+	  string.  http://inamode6.tokuhirom.dnsalias.org/show/1551
+
 Tue Nov 22 18:36:11 2005  Hirokazu Yamamoto  <ocean@m2.ccsnet.ne.jp>
 
 	* win32/win32.c (winnt_stat): set mapped errno instead of ENOENT.
diff --git a/lib/optparse.rb b/lib/optparse.rb
index c056ac8d25..966de0ed68 100644
--- a/lib/optparse.rb
+++ b/lib/optparse.rb
@@ -533,7 +533,7 @@ class OptionParser
     #
     # See OptionParser.accept.
     #
-    def accept(t, pat = /.*/, &block)
+    def accept(t, pat = /.*/nm, &block)
       if pat
         pat.respond_to?(:match) or raise TypeError, "has no `match'"
       else
@@ -1310,7 +1310,7 @@ class OptionParser
       while arg = argv.shift
         case arg
         # long option
-        when /\A--([^=]*)(?:=(.*))?/
+        when /\A--([^=]*)(?:=(.*))?/nm
           opt, rest = $1, $2
           begin
             sw, = complete(:long, opt, true)
@@ -1325,7 +1325,7 @@ class OptionParser
           end
 
         # short option
-        when /\A-(.)((=).*|.+)?/
+        when /\A-(.)((=).*|.+)?/nm
           opt, has_arg, eq, val, rest = $1, $3, $3, $2, $2
           begin
             unless sw = search(:short, opt)
@@ -1545,7 +1545,7 @@ class OptionParser
 : String
   any none-empty string, and no conversion.
 =end #'#"#`#
-  accept(String, /.+/) {|s,*|s}
+  accept(String, /.+/nm) {|s,*|s}
 
 =begin
 : Integer