diff --git a/src/flac/encode.c b/src/flac/encode.c
index e784cd72..8c5a3317 100644
--- a/src/flac/encode.c
+++ b/src/flac/encode.c
@@ -1112,6 +1112,7 @@ FLAC__StreamDecoderWriteStatus verify_write_callback(const FLAC__StreamDecoder *
 				}
 			}
 			FLAC__ASSERT(l < r);
+			FLAC__ASSERT(frame->header.number_type == FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER);
 			fprintf(stderr, "       Absolute sample=%u, frame=%u, channel=%u, sample=%u, expected %d, got %d\n", (unsigned)frame->header.number.sample_number + sample, (unsigned)frame->header.number.sample_number / FLAC__stream_decoder_get_blocksize(decoder), channel, sample, expect, got); /*@@@ WATCHOUT: 4GB limit */
 			return FLAC__STREAM_DECODER_WRITE_ABORT;
 		}
diff --git a/src/libFLAC/file_decoder.c b/src/libFLAC/file_decoder.c
index 7aeaf671..6cf27d83 100644
--- a/src/libFLAC/file_decoder.c
+++ b/src/libFLAC/file_decoder.c
@@ -441,6 +441,8 @@ FLAC__StreamDecoderWriteStatus write_callback_(const FLAC__StreamDecoder *decode
 		FLAC__uint64 next_frame_sample = this_frame_sample + (FLAC__uint64)frame->header.blocksize;
 		FLAC__uint64 target_sample = file_decoder->private->target_sample;
 
+		FLAC__ASSERT(frame->header.number_type == FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER);
+
 		file_decoder->private->last_frame = *frame; /* save the frame in the private */
 		if(this_frame_sample <= target_sample && target_sample < next_frame_sample) { /* we hit our target frame */
 			unsigned delta = (unsigned)(target_sample - this_frame_sample);
@@ -639,6 +641,7 @@ FLAC__bool seek_to_absolute_sample_(FLAC__FileDecoder *decoder, long filesize, F
 		}
 		else { /* we need to narrow the search */
 			FLAC__uint64 this_frame_sample = decoder->private->last_frame.header.number.sample_number;
+			FLAC__ASSERT(decoder->private->last_frame.header.number_type == FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER);
 			if(this_frame_sample == last_frame_sample) {
 				/* our last move backwards wasn't big enough */
 				pos -= (last_pos - pos);
diff --git a/src/libFLAC/stream_decoder.c b/src/libFLAC/stream_decoder.c
index e604e032..0d7bd0ff 100644
--- a/src/libFLAC/stream_decoder.c
+++ b/src/libFLAC/stream_decoder.c
@@ -941,6 +941,7 @@ FLAC__bool stream_decoder_read_frame_(FLAC__StreamDecoder *decoder, FLAC__bool *
 	decoder->protected->sample_rate = decoder->private->frame.header.sample_rate;
 	decoder->protected->blocksize = decoder->private->frame.header.blocksize;
 
+	FLAC__ASSERT(decoder->private->frame.header.number_type == FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER);
 	decoder->private->samples_decoded = decoder->private->frame.header.number.sample_number + decoder->private->frame.header.blocksize;
 
 	/* write it */
@@ -1154,6 +1155,7 @@ FLAC__bool stream_decoder_read_frame_header_(FLAC__StreamDecoder *decoder)
 			decoder->protected->state = FLAC__STREAM_DECODER_SEARCH_FOR_FRAME_SYNC;
 			return true;
 		}
+		decoder->private->frame.header.number_type = FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER;
 		decoder->private->frame.header.number.sample_number = xx;
 	}
 	else {
@@ -1168,6 +1170,7 @@ FLAC__bool stream_decoder_read_frame_header_(FLAC__StreamDecoder *decoder)
 		}
 		decoder->private->last_frame_number = x;
 		if(decoder->private->has_stream_info) {
+			decoder->private->frame.header.number_type = FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER;
 			decoder->private->frame.header.number.sample_number = (FLAC__int64)decoder->private->stream_info.data.stream_info.min_blocksize * (FLAC__int64)x;
 		}
 		else {
diff --git a/src/libFLAC/stream_encoder_framing.c b/src/libFLAC/stream_encoder_framing.c
index 036ffd2c..3775ff87 100644
--- a/src/libFLAC/stream_encoder_framing.c
+++ b/src/libFLAC/stream_encoder_framing.c
@@ -222,6 +222,7 @@ FLAC__bool FLAC__frame_add_header(const FLAC__FrameHeader *header, FLAC__bool st
 	if(!FLAC__bitbuffer_write_raw_uint32(bb, 0, FLAC__FRAME_HEADER_ZERO_PAD_LEN))
 		return false;
 
+	FLAC__ASSERT(header->number_type == FLAC__FRAME_NUMBER_TYPE_FRAME_NUMBER);
 	if(!FLAC__bitbuffer_write_utf8_uint32(bb, header->number.frame_number))
 		return false;