diff --git a/libavformat/asf.c b/libavformat/asf.c
index f63e4b6959..e6a38c953a 100644
--- a/libavformat/asf.c
+++ b/libavformat/asf.c
@@ -203,8 +203,10 @@ static int asf_read_header(AVFormatContext *s, AVFormatParameters *ap)
                 goto fail;
             st->priv_data = asf_st;
             st->start_time = asf->hdr.preroll;
-            st->duration = asf->hdr.send_time /
-                (10000000 / 1000) - st->start_time;
+            if(!(asf->hdr.flags & 0x01)) { // if we aren't streaming...
+                st->duration = asf->hdr.send_time /
+                    (10000000 / 1000) - st->start_time;
+            }
             get_guid(pb, &g);
 
             test_for_ext_stream_audio = 0;
@@ -328,7 +330,8 @@ static int asf_read_header(AVFormatContext *s, AVFormatParameters *ap)
             url_fskip(pb, gsize - (pos2 - pos1 + 24));
         } else if (!memcmp(&g, &data_header, sizeof(GUID))) {
             asf->data_object_offset = url_ftell(pb);
-            if (gsize != (uint64_t)-1 && gsize >= 24) {
+            // if not streaming, gsize is not unlimited (how?), and there is enough space in the file..
+            if (!(asf->hdr.flags & 0x01) && gsize != (uint64_t)-1 && gsize >= 24) {
                 asf->data_object_size = gsize - 24;
             } else {
                 asf->data_object_size = (uint64_t)-1;
diff --git a/libavformat/asf.h b/libavformat/asf.h
index bbe88801a8..5e3d26c399 100644
--- a/libavformat/asf.h
+++ b/libavformat/asf.h
@@ -86,7 +86,7 @@ typedef struct {
     int asfid2avid[128];        /* conversion table from asf ID 2 AVStream ID */
     ASFStream streams[128];     /* it's max number and it's not that big */
     /* non streamed additonnal info */
-    int64_t nb_packets;
+    uint64_t nb_packets;
     int64_t duration; /* in 100ns units */
     /* packet filling */
     unsigned char multi_payloads_present;