diff --git a/ChangeLog b/ChangeLog
index f77871d28f..71e06cb2e7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Sun Mar 14 02:40:38 2010  Tanaka Akira  <akr@fsij.org>
+
+	* tool/transcode-tblgen.rb: reject ambiguous mapping.
+
+	* enc/trans/single_byte.trans: remove ambiguous maping such as
+	  \xD6 -> U+05F2 and \xD6\xC7 -> U+FB1F in Windows-1255
+
 Sat Mar 13 23:48:27 2010  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* file.c (file_expand_path): should not just copy the encoding
diff --git a/enc/trans/single_byte.trans b/enc/trans/single_byte.trans
index 0d42740d30..db47074570 100644
--- a/enc/trans/single_byte.trans
+++ b/enc/trans/single_byte.trans
@@ -24,7 +24,7 @@
     tbl_to_ucs = control1_if_needed + eval(name.gsub(/-/, '_') + "_TO_UCS_TBL")
     set_valid_byte_pattern(name, '1byte')
     code = ''
-    code << transcode_tblgen(name, "UTF-8", [["{00-7f}", :nomap], *tbl_to_ucs])
+    code << transcode_tblgen(name, "UTF-8", [["{00-7f}", :nomap], *tbl_to_ucs.reject {|a, b| a.length != 2 }])
     code << "\n"
     code << transcode_tblgen("UTF-8", name, [["{00-7f}", :nomap], *tbl_to_ucs.map {|a,b| [b,a] }])
     code
diff --git a/tool/transcode-tblgen.rb b/tool/transcode-tblgen.rb
index dbd03e3028..14a09dbadf 100755
--- a/tool/transcode-tblgen.rb
+++ b/tool/transcode-tblgen.rb
@@ -133,6 +133,12 @@ class StrSet
     }
   end
 
+  def has_nonempty?
+    @pat.any? {|seq|
+      !seq.empty?
+    }
+  end
+
   def first_bytes
     result = {}
     @pat.each {|seq|
@@ -228,6 +234,18 @@ class ActionMap
     @map.keys.map {|k| k.max_length }.max
   end
 
+  def check_conflict
+    has_empty = false
+    has_nonempty = false
+    @map.each {|ss, action|
+      has_empty = true if ss.emptyable?
+      has_nonempty = true if ss.has_nonempty?
+    }
+    if has_empty && has_nonempty
+      raise "conflict between empty and nonempty sequence"
+    end
+  end
+
   def empty_action
     @map.each {|ss, action|
       return action if ss.emptyable?
@@ -440,6 +458,7 @@ End
 
     table = Array.new(0x100, :invalid)
     each_firstbyte(valid_encoding) {|byte, rest, rest_valid_encoding|
+      rest.check_conflict
       if a = rest.empty_action
         table[byte] = a
       else