diff --git a/src/decoder/plugins/AudiofileDecoderPlugin.cxx b/src/decoder/plugins/AudiofileDecoderPlugin.cxx
index 93a6e03a2..5accff034 100644
--- a/src/decoder/plugins/AudiofileDecoderPlugin.cxx
+++ b/src/decoder/plugins/AudiofileDecoderPlugin.cxx
@@ -184,7 +184,7 @@ audiofile_setup_sample_format(AFfilehandle af_fp)
 static void
 audiofile_stream_decode(Decoder &decoder, InputStream &is)
 {
-	if (!is.IsSeekable()) {
+	if (!is.IsSeekable() || !is.KnownSize()) {
 		LogWarning(audiofile_domain, "not seekable");
 		return;
 	}
@@ -250,7 +250,7 @@ gcc_pure
 static int
 audiofile_get_duration(InputStream &is)
 {
-	if (!is.IsSeekable())
+	if (!is.IsSeekable() || !is.KnownSize())
 		return -1;
 
 	AudioFileInputStream afis{nullptr, is};