diff --git a/libavformat/vorbiscomment.c b/libavformat/vorbiscomment.c
index cc9b6620ef..e953d83d65 100644
--- a/libavformat/vorbiscomment.c
+++ b/libavformat/vorbiscomment.c
@@ -61,8 +61,10 @@ int ff_vorbiscomment_write(uint8_t **p, AVDictionary **m,
         AVDictionaryEntry *tag = NULL;
         bytestream_put_le32(p, count);
         while ((tag = av_dict_get(*m, "", tag, AV_DICT_IGNORE_SUFFIX))) {
-            unsigned int len1 = strlen(tag->key);
-            unsigned int len2 = strlen(tag->value);
+            int64_t len1 = strlen(tag->key);
+            int64_t len2 = strlen(tag->value);
+            if (len1+1+len2 > UINT32_MAX)
+                return AVERROR(EINVAL);
             bytestream_put_le32(p, len1+1+len2);
             bytestream_put_buffer(p, tag->key, len1);
             bytestream_put_byte(p, '=');