diff --git a/libavformat/img2.c b/libavformat/img2.c
index 00c5013015..98397f4dcb 100644
--- a/libavformat/img2.c
+++ b/libavformat/img2.c
@@ -284,7 +284,7 @@ static int read_header(AVFormatContext *s1, AVFormatParameters *ap)
         s->split_planes = str && !av_strcasecmp(str + 1, "y");
         st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
         st->codec->codec_id = av_str2id(img_tags, s->path);
-        if (st->codec->codec_id = CODEC_ID_LJPEG)
+        if (st->codec->codec_id == CODEC_ID_LJPEG)
             st->codec->codec_id = CODEC_ID_MJPEG;
     }
     if(st->codec->codec_type == AVMEDIA_TYPE_VIDEO && pix_fmt != PIX_FMT_NONE)