diff --git a/NEWS b/NEWS
index 83a168029..cff37aeee 100644
--- a/NEWS
+++ b/NEWS
@@ -1,4 +1,6 @@
 ver 0.18.1 (2013/11/??)
+* filter:
+  - autoconvert: fix "volume_normalization" with mp3 files
 
 ver 0.18 (2013/10/31)
 * configuration:
diff --git a/src/filter/AutoConvertFilterPlugin.cxx b/src/filter/AutoConvertFilterPlugin.cxx
index 4b5ebff4d..918a16e53 100644
--- a/src/filter/AutoConvertFilterPlugin.cxx
+++ b/src/filter/AutoConvertFilterPlugin.cxx
@@ -60,8 +60,8 @@ AutoConvertFilter::Open(AudioFormat &in_audio_format, Error &error)
 
 	/* open the "real" filter */
 
-	const AudioFormat child_audio_format = in_audio_format;
-	AudioFormat out_audio_format = filter->Open(in_audio_format, error);
+	AudioFormat child_audio_format = in_audio_format;
+	AudioFormat out_audio_format = filter->Open(child_audio_format, error);
 	if (!out_audio_format.IsDefined())
 		return out_audio_format;