diff --git a/libavcodec/lagarith.c b/libavcodec/lagarith.c
index 0611abfef4..d0a5049542 100644
--- a/libavcodec/lagarith.c
+++ b/libavcodec/lagarith.c
@@ -569,7 +569,7 @@ static int lag_decode_frame(AVCodecContext *avctx,
 
         if (!l->rgb_planes) {
             l->rgb_stride = FFALIGN(avctx->width, 16);
-            l->rgb_planes = av_malloc(l->rgb_stride * avctx->height * planes + 16);
+            l->rgb_planes = av_malloc(l->rgb_stride * avctx->height * 4 + 16);
             if (!l->rgb_planes) {
                 av_log(avctx, AV_LOG_ERROR, "cannot allocate temporary buffer\n");
                 return AVERROR(ENOMEM);