diff --git a/src/decoder/plugins/FlacCommon.cxx b/src/decoder/plugins/FlacCommon.cxx
index a3b1e9184..8aa84201d 100644
--- a/src/decoder/plugins/FlacCommon.cxx
+++ b/src/decoder/plugins/FlacCommon.cxx
@@ -33,7 +33,7 @@ flac_data::flac_data(Decoder &_decoder,
 		     InputStream &_input_stream)
 	:FlacInput(_input_stream, &_decoder),
 	 initialized(false), unsupported(false),
-	 total_frames(0), position(0),
+	 position(0),
 	 decoder(_decoder), input_stream(_input_stream)
 {
 }
@@ -142,6 +142,7 @@ flac_got_first_frame(struct flac_data *data, const FLAC__FrameHeader *header)
 			    data->input_stream.IsSeekable(),
 			    duration);
 
+	data->total_frames = 0; /* unkown duration */
 	data->initialized = true;
 
 	return true;
diff --git a/src/decoder/plugins/FlacCommon.hxx b/src/decoder/plugins/FlacCommon.hxx
index b5de6974d..2d424cbe5 100644
--- a/src/decoder/plugins/FlacCommon.hxx
+++ b/src/decoder/plugins/FlacCommon.hxx
@@ -56,6 +56,8 @@ struct flac_data : public FlacInput {
 
 	/**
 	 * The total number of frames in this song.  0 means unknown.
+	 *
+	 * This attribute is defined if "initialized" is true.
 	 */
 	FLAC__uint64 total_frames;