diff --git a/src/decoder_api.c b/src/decoder_api.c
index 4e34db71d..da61f3110 100644
--- a/src/decoder_api.c
+++ b/src/decoder_api.c
@@ -197,6 +197,7 @@ decoder_data(struct decoder *decoder,
 	char *data;
 
 	assert(dc.state == DECODE_STATE_DECODE);
+	assert(length % audio_format_frame_size(&dc.in_audio_format) == 0);
 
 	if (dc.command == DECODE_COMMAND_STOP ||
 	    dc.command == DECODE_COMMAND_SEEK ||