diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 4d02488b19787b2caf2c0a9fda76bcd0eef18b68..eadf65302873107f47cfcbbec263968c2a71ee6a 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -639,16 +639,19 @@ static int ebml_read_float(AVIOContext *pb, int size, double *num)
  */
 static int ebml_read_ascii(AVIOContext *pb, int size, char **str)
 {
-    av_free(*str);
+    char *res;
+
     /* EBML strings are usually not 0-terminated, so we allocate one
      * byte more, read the string and NULL-terminate it ourselves. */
-    if (!(*str = av_malloc(size + 1)))
+    if (!(res = av_malloc(size + 1)))
         return AVERROR(ENOMEM);
-    if (avio_read(pb, (uint8_t *) *str, size) != size) {
-        av_freep(str);
+    if (avio_read(pb, (uint8_t *) res, size) != size) {
+        av_free(res);
         return AVERROR(EIO);
     }
-    (*str)[size] = '\0';
+    (res)[size] = '\0';
+    av_free(*str);
+    *str = res;
 
     return 0;
 }