diff --git a/test/encode/avcenc.c b/test/encode/avcenc.c
index fafb366..84d217a 100644
--- a/test/encode/avcenc.c
+++ b/test/encode/avcenc.c
@@ -1414,6 +1414,8 @@
     seq_param->picture_width_in_mbs = width_in_mbs;
     seq_param->picture_height_in_mbs = height_in_mbs;
     seq_param->seq_fields.bits.frame_mbs_only_flag = 1;
+    seq_param->seq_fields.bits.chroma_format_idc = 1;
+
     
     if (frame_bit_rate > 0)
         seq_param->bits_per_second = 1024 * frame_bit_rate; /* use kbps as input */