diff --git a/libavcodec/sunrast.c b/libavcodec/sunrast.c
index 3e1cea6c36..c33265dc84 100644
--- a/libavcodec/sunrast.c
+++ b/libavcodec/sunrast.c
@@ -93,7 +93,7 @@ static int sunrast_decode_frame(AVCodecContext *avctx, void *data,
             avctx->pix_fmt = PIX_FMT_MONOWHITE;
             break;
         case 8:
-            avctx->pix_fmt = PIX_FMT_PAL8;
+            avctx->pix_fmt = maplength ? PIX_FMT_PAL8 : PIX_FMT_GRAY8;
             break;
         case 24:
             avctx->pix_fmt = (type == RT_FORMAT_RGB) ? PIX_FMT_RGB24 : PIX_FMT_BGR24;
@@ -121,7 +121,7 @@ static int sunrast_decode_frame(AVCodecContext *avctx, void *data,
     if (depth != 8 && maplength) {
         av_log(avctx, AV_LOG_WARNING, "useless colormap found or file is corrupted, trying to recover\n");
 
-    } else if (depth == 8) {
+    } else if (maplength) {
         unsigned int len = maplength / 3;
 
         if (!maplength) {