diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
index 6e18a4a23e..0969b12e7f 100644
--- a/fftools/ffmpeg_opt.c
+++ b/fftools/ffmpeg_opt.c
@@ -898,8 +898,11 @@ static void add_input_streams(OptionsContext *o, AVFormatContext *ic)
         MATCH_PER_STREAM_OPT(codec_tags, str, codec_tag, ic, st);
         if (codec_tag) {
             uint32_t tag = strtol(codec_tag, &next, 0);
-            if (*next)
-                tag = AV_RL32(codec_tag);
+            if (*next) {
+                uint8_t buf[4] = { 0 };
+                memcpy(buf, codec_tag, FFMIN(sizeof(buf), strlen(codec_tag)));
+                tag = AV_RL32(buf);
+            }
             st->codecpar->codec_tag = tag;
         }
 
@@ -1660,8 +1663,11 @@ static OutputStream *new_output_stream(OptionsContext *o, AVFormatContext *oc, e
     MATCH_PER_STREAM_OPT(codec_tags, str, codec_tag, oc, st);
     if (codec_tag) {
         uint32_t tag = strtol(codec_tag, &next, 0);
-        if (*next)
-            tag = AV_RL32(codec_tag);
+        if (*next) {
+            uint8_t buf[4] = { 0 };
+            memcpy(buf, codec_tag, FFMIN(sizeof(buf), strlen(codec_tag)));
+            tag = AV_RL32(buf);
+        }
         ost->st->codecpar->codec_tag =
         ost->enc_ctx->codec_tag = tag;
     }