diff --git a/libavcodec/shorten.c b/libavcodec/shorten.c
index 89346b4aad..0b4a473892 100644
--- a/libavcodec/shorten.c
+++ b/libavcodec/shorten.c
@@ -84,7 +84,7 @@ typedef struct ShortenContext {
     GetBitContext gb;
 
     int min_framesize, max_framesize;
-    int channels;
+    unsigned channels;
 
     int32_t *decoded[MAX_CHANNELS];
     int32_t *decoded_base[MAX_CHANNELS];
@@ -343,7 +343,11 @@ static int read_header(ShortenContext *s)
     s->internal_ftype = get_uint(s, TYPESIZE);
 
     s->channels = get_uint(s, CHANSIZE);
-    if (s->channels <= 0 || s->channels > MAX_CHANNELS) {
+    if (!s->channels) {
+        av_log(s->avctx, AV_LOG_ERROR, "No channels reported\n");
+        return AVERROR_INVALIDDATA;
+    }
+    if (s->channels > MAX_CHANNELS) {
         av_log(s->avctx, AV_LOG_ERROR, "too many channels: %d\n", s->channels);
         s->channels = 0;
         return AVERROR_INVALIDDATA;
@@ -352,7 +356,8 @@ static int read_header(ShortenContext *s)
 
     /* get blocksize if version > 0 */
     if (s->version > 0) {
-        int skip_bytes, blocksize;
+        int skip_bytes;
+        unsigned blocksize;
 
         blocksize = get_uint(s, av_log2(DEFAULT_BLOCK_SIZE));
         if (!blocksize || blocksize > MAX_BLOCKSIZE) {
@@ -504,7 +509,7 @@ static int shorten_decode_frame(AVCodecContext *avctx, void *data,
                 s->bitshift = get_ur_golomb_shorten(&s->gb, BITSHIFTSIZE);
                 break;
             case FN_BLOCKSIZE: {
-                int blocksize = get_uint(s, av_log2(s->blocksize));
+                unsigned blocksize = get_uint(s, av_log2(s->blocksize));
                 if (blocksize > s->blocksize) {
                     av_log(avctx, AV_LOG_ERROR,
                            "Increasing block size is not supported\n");