diff --git a/src/h265.c b/src/h265.c
index a3baa3c..26f4881 100644
--- a/src/h265.c
+++ b/src/h265.c
@@ -381,6 +381,15 @@ static void h265_fill_slice_params(VAPictureParameterBufferHEVC *picture,
 				H265_NUH_TEMPORAL_ID_PLUS1_MASK;
 
 	slice_params->bit_size = slice->slice_data_size * 8;
+	if (getenv("LIBVA_HEVC_DIAG")) {
+		request_log("hevc_diag: slice_data_size=%u slice_data_offset=%u "
+			    "slice_data_byte_offset=%u slice_data_flag=%u source_offset=%u\n",
+			    (unsigned)slice->slice_data_size,
+			    (unsigned)slice->slice_data_offset,
+			    (unsigned)slice->slice_data_byte_offset,
+			    (unsigned)slice->slice_data_flag,
+			    source_offset);
+	}
 
 	/* C1: data_byte_offset, NOT data_bit_offset. Plain byte offset to
 	 * the first byte of slice segment header data within the OUTPUT