diff --git a/tool/transcode-tblgen.rb b/tool/transcode-tblgen.rb
index edf8f23468..dc1c4062e9 100644
--- a/tool/transcode-tblgen.rb
+++ b/tool/transcode-tblgen.rb
@@ -725,7 +725,7 @@ def citrus_decode_mapsrc(ces, csid, mapsrcs)
     path << ".src"
     path[path.rindex('/')] = '%'
     STDERR.puts 'load mapsrc %s' % path if VERBOSE_MODE
-    open(path) do |f|
+    open(path, 'rb') do |f|
       f.each_line do |l|
         break if /^BEGIN_MAP/ =~ l
       end