diff --git a/libavcodec/pnmdec.c b/libavcodec/pnmdec.c
index a6945549bd..59013ada49 100644
--- a/libavcodec/pnmdec.c
+++ b/libavcodec/pnmdec.c
@@ -262,7 +262,7 @@ static int pnm_decode_frame(AVCodecContext *avctx, AVFrame *p,
         break;
     case AV_PIX_FMT_GBRPF32:
         if (!s->half) {
-            if (avctx->width * avctx->height * 12 > s->bytestream_end - s->bytestream)
+            if (avctx->width * avctx->height * 12LL > s->bytestream_end - s->bytestream)
                 return AVERROR_INVALIDDATA;
             scale = 1.f / s->scale;
             if (s->endian) {