diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 44f8e6b771..d21906b406 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -3826,7 +3826,7 @@ static int mov_write_header(AVFormatContext *s)
         if (!(mov->flags & (FF_MOV_FLAG_FRAG_KEYFRAME |
                             FF_MOV_FLAG_FRAG_CUSTOM)) &&
             !mov->max_fragment_duration && !mov->max_fragment_size)
-            mov->max_fragment_duration = 5000000;
+            mov->flags |= FF_MOV_FLAG_FRAG_KEYFRAME;
     }
 
     if (mov->reserved_moov_size){
diff --git a/tests/ref/lavf/ismv b/tests/ref/lavf/ismv
index 458c4c1b56..dd4b162d4e 100644
--- a/tests/ref/lavf/ismv
+++ b/tests/ref/lavf/ismv
@@ -1,9 +1,9 @@
-1efcfb3f09a9802ba63f6f592601281e *./tests/data/lavf/lavf.ismv
-312255 ./tests/data/lavf/lavf.ismv
+ec3e7d37755378cbe9907175768afbac *./tests/data/lavf/lavf.ismv
+312453 ./tests/data/lavf/lavf.ismv
 ./tests/data/lavf/lavf.ismv CRC=0x9d9a638a
-95a3553714bb603f6b0e2bc0fc3fb319 *./tests/data/lavf/lavf.ismv
-321181 ./tests/data/lavf/lavf.ismv
+a4b6fb1f46848622477230f69040942c *./tests/data/lavf/lavf.ismv
+321359 ./tests/data/lavf/lavf.ismv
 ./tests/data/lavf/lavf.ismv CRC=0xe8130120
-1efcfb3f09a9802ba63f6f592601281e *./tests/data/lavf/lavf.ismv
-312255 ./tests/data/lavf/lavf.ismv
+ec3e7d37755378cbe9907175768afbac *./tests/data/lavf/lavf.ismv
+312453 ./tests/data/lavf/lavf.ismv
 ./tests/data/lavf/lavf.ismv CRC=0x9d9a638a