diff --git a/src/http/modules/ngx_http_mp4_module.c b/src/http/modules/ngx_http_mp4_module.c
index 8f439ba92..980bf5719 100644
--- a/src/http/modules/ngx_http_mp4_module.c
+++ b/src/http/modules/ngx_http_mp4_module.c
@@ -1840,7 +1840,7 @@ ngx_http_mp4_read_smhd_atom(ngx_http_mp4_file_t *mp4, uint64_t atom_data_size)
     atom->pos = atom_header;
     atom->last = atom_header + atom_size;
 
-    trak->vmhd_size += atom_size;
+    trak->smhd_size += atom_size;
     trak->out[NGX_HTTP_MP4_SMHD_ATOM].buf = atom;
 
     ngx_mp4_atom_next(mp4, atom_data_size);