diff --git a/libavcodec/sanm.c b/libavcodec/sanm.c
index 642ef02bff..02bb78859a 100644
--- a/libavcodec/sanm.c
+++ b/libavcodec/sanm.c
@@ -1670,6 +1670,8 @@ static int process_frame_obj(SANMVideoContext *ctx, GetByteContext *gb)
             /* Rebel Assault 1: 384x242 internal size */
             xres = 384;
             yres = 242;
+            if (w > xres || h > yres)
+                return AVERROR_INVALIDDATA;
             ctx->have_dimensions = 1;
         } else if (codec == 37 || codec == 47 || codec == 48) {
             /* these codecs work on full frames, trust their dimensions */