diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 61f397b5d0..0b4669bdf3 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -3609,10 +3609,23 @@ static int mov_write_header(AVFormatContext *s)
     AVDictionaryEntry *t, *global_tcr = av_dict_get(s->metadata, "timecode", NULL, 0);
     int i, hint_track = 0, tmcd_track = 0;
 
+    /* Default mode == MP4 */
+    mov->mode = MODE_MP4;
+
+    if (s->oformat != NULL) {
+        if (!strcmp("3gp", s->oformat->name)) mov->mode = MODE_3GP;
+        else if (!strcmp("3g2", s->oformat->name)) mov->mode = MODE_3GP|MODE_3G2;
+        else if (!strcmp("mov", s->oformat->name)) mov->mode = MODE_MOV;
+        else if (!strcmp("psp", s->oformat->name)) mov->mode = MODE_PSP;
+        else if (!strcmp("ipod",s->oformat->name)) mov->mode = MODE_IPOD;
+        else if (!strcmp("ismv",s->oformat->name)) mov->mode = MODE_ISM;
+        else if (!strcmp("f4v", s->oformat->name)) mov->mode = MODE_F4V;
+    }
+
     /* Set the FRAGMENT flag if any of the fragmentation methods are
      * enabled. */
     if (mov->max_fragment_duration || mov->max_fragment_size ||
-        (s->oformat && !strcmp(s->oformat->name, "ismv")) ||
+        mov->mode == MODE_ISM ||
         mov->flags & (FF_MOV_FLAG_EMPTY_MOOV |
                       FF_MOV_FLAG_FRAG_KEYFRAME |
                       FF_MOV_FLAG_FRAG_CUSTOM))
@@ -3641,17 +3654,6 @@ static int mov_write_header(AVFormatContext *s)
         return -1;
     }
 
-    /* Default mode == MP4 */
-    mov->mode = MODE_MP4;
-
-    if (!strcmp("3gp", s->oformat->name)) mov->mode = MODE_3GP;
-    else if (!strcmp("3g2", s->oformat->name)) mov->mode = MODE_3GP|MODE_3G2;
-    else if (!strcmp("mov", s->oformat->name)) mov->mode = MODE_MOV;
-    else if (!strcmp("psp", s->oformat->name)) mov->mode = MODE_PSP;
-    else if (!strcmp("ipod",s->oformat->name)) mov->mode = MODE_IPOD;
-    else if (!strcmp("ismv",s->oformat->name)) mov->mode = MODE_ISM;
-    else if (!strcmp("f4v", s->oformat->name)) mov->mode = MODE_F4V;
-
     mov_write_ftyp_tag(pb,s);
     if (mov->mode == MODE_PSP) {
         int video_streams_nb = 0, audio_streams_nb = 0, other_streams_nb = 0;