diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index f189741af6..9c545c08d0 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -398,7 +398,7 @@ typedef struct AVProbeData {
     const char *filename;
     unsigned char *buf; /**< Buffer must have AVPROBE_PADDING_SIZE of extra allocated bytes filled with zero. */
     int buf_size;       /**< Size of buf except extra allocated bytes */
-    uint8_t *mime_type; /**< mime_type, when known. */
+    const char *mime_type; /**< mime_type, when known. */
 } AVProbeData;
 
 #define AVPROBE_SCORE_RETRY (AVPROBE_SCORE_MAX/4)
diff --git a/libavformat/format.c b/libavformat/format.c
index 2d56e6d545..527299d652 100644
--- a/libavformat/format.c
+++ b/libavformat/format.c
@@ -243,6 +243,7 @@ int av_probe_input_buffer2(AVIOContext *pb, AVInputFormat **fmt,
     int ret = 0, probe_size, buf_offset = 0;
     int score = 0;
     int ret2;
+    uint8_t *mime_type_opt = NULL;
 
     if (!max_probe_size)
         max_probe_size = PROBE_BUF_MAX;
@@ -255,8 +256,11 @@ int av_probe_input_buffer2(AVIOContext *pb, AVInputFormat **fmt,
     if (offset >= max_probe_size)
         return AVERROR(EINVAL);
 
-    if (pb->av_class)
-        av_opt_get(pb, "mime_type", AV_OPT_SEARCH_CHILDREN, &pd.mime_type);
+    if (pb->av_class) {
+        av_opt_get(pb, "mime_type", AV_OPT_SEARCH_CHILDREN, &mime_type_opt);
+        pd.mime_type = (const char *)mime_type_opt;
+        mime_type_opt = NULL;
+    }
 #if 0
     if (!*fmt && pb->av_class && av_opt_get(pb, "mime_type", AV_OPT_SEARCH_CHILDREN, &mime_type) >= 0 && mime_type) {
         if (!av_strcasecmp(mime_type, "audio/aacp")) {
@@ -320,7 +324,7 @@ fail:
     if (ret >= 0)
         ret = ret2;
 
-    av_free(pd.mime_type);
+    av_freep(&pd.mime_type);
     return ret < 0 ? ret : score;
 }