diff --git a/libavformat/nut.c b/libavformat/nut.c
index aee1606edb..2d63cc7ba7 100644
--- a/libavformat/nut.c
+++ b/libavformat/nut.c
@@ -328,10 +328,10 @@ static int get_packetheader(NUTContext *nut, ByteIOContext *bc, int calculate_ch
     int64_t start, size;
     start= url_ftell(bc) - 8;
 
-    init_checksum(bc, calculate_checksum ? update_adler32 : NULL, 0);
-
     size= get_v(bc);
 
+    init_checksum(bc, calculate_checksum ? update_adler32 : NULL, 0);
+
     nut->packet_start[2] = start;
     nut->written_packet_size= size;
 
@@ -465,12 +465,12 @@ static int put_packetheader(NUTContext *nut, ByteIOContext *bc, int max_size, in
     nut->packet_start[2]= url_ftell(bc) - 8;
     nut->written_packet_size = max_size;
     
-    if(calculate_checksum)
-        init_checksum(bc, update_adler32, 0);
-
     /* packet header */
     put_v(bc, nut->written_packet_size); /* forward ptr */
 
+    if(calculate_checksum)
+        init_checksum(bc, update_adler32, 0);
+
     return 0;
 }