diff --git a/libavformat/iamf_parse.c b/libavformat/iamf_parse.c
index 00190d87a4..2394536f72 100644
--- a/libavformat/iamf_parse.c
+++ b/libavformat/iamf_parse.c
@@ -539,7 +539,8 @@ static int param_parse(void *s, IAMFContext *c, AVIOContext *pb,
         if (constant_subblock_duration == 0) {
             subblock_duration = ffio_read_leb(pb);
             total_duration += subblock_duration;
-        }
+        } else if (i == nb_subblocks - 1)
+            subblock_duration = duration - i * constant_subblock_duration;
 
         switch (type) {
         case AV_IAMF_PARAMETER_DEFINITION_MIX_GAIN: {
diff --git a/libavformat/iamf_reader.c b/libavformat/iamf_reader.c
index 7ad61cb246..9f3469b64f 100644
--- a/libavformat/iamf_reader.c
+++ b/libavformat/iamf_reader.c
@@ -178,7 +178,8 @@ static int parameter_block_obu(AVFormatContext *s, IAMFDemuxContext *c,
         if (!param_definition->mode && !constant_subblock_duration) {
             subblock_duration = ffio_read_leb(pb);
             total_duration += subblock_duration;
-        }
+        } else if (i == nb_subblocks - 1)
+            subblock_duration = duration - i * constant_subblock_duration;
 
         switch (param->type) {
         case AV_IAMF_PARAMETER_DEFINITION_MIX_GAIN: {