diff --git a/libavcodec/sanm.c b/libavcodec/sanm.c
index 2a04706c2e..c39d269a41 100644
--- a/libavcodec/sanm.c
+++ b/libavcodec/sanm.c
@@ -802,7 +802,7 @@ static int draw_glyph(SANMVideoContext *ctx, uint16_t *dst, int index, uint16_t
     uint16_t colors[2] = { fg_color, bg_color };
     int x, y;
 
-    if (index > NGLYPHS) {
+    if (index >= NGLYPHS) {
         av_log(ctx->avctx, AV_LOG_ERROR, "ignoring nonexistent glyph #%u\n", index);
         return AVERROR_INVALIDDATA;
     }