diff --git a/libavcodec/cbs_mpeg2.c b/libavcodec/cbs_mpeg2.c
index 1f1197fb30..ce22e32c15 100644
--- a/libavcodec/cbs_mpeg2.c
+++ b/libavcodec/cbs_mpeg2.c
@@ -251,9 +251,7 @@ static int cbs_mpeg2_read_unit(CodedBitstreamContext *ctx,
                   group_of_pictures_header, NULL);
 #undef START
         default:
-            av_log(ctx->log_ctx, AV_LOG_ERROR, "Unknown start code %02"PRIx32".\n",
-                   unit->type);
-            return AVERROR_INVALIDDATA;
+            return AVERROR(ENOSYS);
         }
     }
 
diff --git a/libavcodec/cbs_mpeg2_syntax_template.c b/libavcodec/cbs_mpeg2_syntax_template.c
index 09487fe56d..d753cdc901 100644
--- a/libavcodec/cbs_mpeg2_syntax_template.c
+++ b/libavcodec/cbs_mpeg2_syntax_template.c
@@ -335,9 +335,9 @@ static int FUNC(extension_data)(CodedBitstreamContext *ctx, RWContext *rw,
         return FUNC(picture_coding_extension)
             (ctx, rw, &current->data.picture_coding);
     default:
-        av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid extension ID %d.\n",
+        av_log(ctx->log_ctx, AV_LOG_ERROR, "Extension ID %d not supported.\n",
                current->extension_start_code_identifier);
-        return AVERROR_INVALIDDATA;
+        return AVERROR_PATCHWELCOME;
     }
 }