diff --git a/libavformat/isom.h b/libavformat/isom.h
index 07f09d6eff..c0a5788e08 100644
--- a/libavformat/isom.h
+++ b/libavformat/isom.h
@@ -193,7 +193,7 @@ typedef struct MOVStreamContext {
     unsigned int sample_size; ///< may contain value calculated from stsd or value from stsz atom
     unsigned int stsz_sample_size; ///< always contains sample size from stsz atom
     unsigned int sample_count;
-    int *sample_sizes;
+    unsigned int *sample_sizes;
     int keyframe_absent;
     unsigned int keyframe_count;
     int *keyframes;
diff --git a/libavformat/mov.c b/libavformat/mov.c
index 6174a04c31..45eca74d1d 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -3308,9 +3308,9 @@ static int mov_read_stsz(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
     for (i = 0; i < entries; i++) {
         sc->sample_sizes[i] = get_bits_long(&gb, field_size);
-        if (sc->sample_sizes[i] < 0) {
+        if (sc->sample_sizes[i] > INT64_MAX - sc->data_size) {
             av_free(buf);
-            av_log(c->fc, AV_LOG_ERROR, "Invalid sample size %d\n", sc->sample_sizes[i]);
+            av_log(c->fc, AV_LOG_ERROR, "Sample size overflow in STSZ\n");
             return AVERROR_INVALIDDATA;
         }
         sc->data_size += sc->sample_sizes[i];