diff --git a/src/file_x4a.c b/src/file_x4a.c
index b665e319..9c6f463d 100644
--- a/src/file_x4a.c
+++ b/src/file_x4a.c
@@ -32,7 +32,7 @@
 #include "filegen.h"
 #include "common.h"
 
-/*@ requires \valid(file_stat); */
+/*@ requires valid_register_header_check(file_stat); */
 static void register_header_check_ysfc100(file_stat_t *file_stat);
 
 const file_hint_t file_hint_x4a = {
@@ -51,22 +51,18 @@ struct x4a_catalog
 } __attribute__((gcc_struct, __packed__));
 
 /*@
-  @ requires \valid(fr);
-  @ requires valid_file_recovery(fr);
-  @ requires \separated(fr, fr->handle, fr->extension, &errno, &Frama_C_entropy_source);
   @ requires fr->file_check == &file_check_x4a;
-  @ ensures \valid(fr->handle);
+  @ requires valid_file_check_param(fr);
+  @ ensures  valid_file_check_result(fr);
   @ assigns *fr->handle, errno, fr->file_size;
   @ assigns Frama_C_entropy_source;
   @*/
 static void file_check_x4a(file_recovery_t *fr)
 {
-  unsigned char buffer[0x200];
+  char buffer[0x200];
   unsigned int i;
   unsigned int fs = 0x80;
   fr->file_size = 0;
-  fr->offset_error = 0;
-  fr->offset_ok = 0;
   if(my_fseek(fr->handle, 0, SEEK_SET) < 0 || fread(&buffer, sizeof(buffer), 1, fr->handle) != 1)
     return;
 #ifdef __FRAMAC__
@@ -83,8 +79,6 @@ static void file_check_x4a(file_recovery_t *fr)
     if(tmp > fs)
       fs = tmp;
   }
-  if(my_fseek(fr->handle, 0, SEEK_SET) < 0 || fread(&buffer, 8, 1, fr->handle) != 1)
-    return;
   {
     const struct x4a_catalog *p = (const struct x4a_catalog *)buffer;
     fr->file_size = (uint64_t)fs + be32(p->size);
@@ -93,12 +87,9 @@ static void file_check_x4a(file_recovery_t *fr)
 
 /*@
   @ requires buffer_size >= 0x34;
-  @ requires \valid_read(buffer+(0..buffer_size-1));
-  @ requires valid_file_recovery(file_recovery);
-  @ requires \valid(file_recovery_new);
-  @ requires file_recovery_new->blocksize > 0;
   @ requires separation: \separated(&file_hint_x4a, buffer+(..), file_recovery, file_recovery_new);
-  @ ensures  \result!=0 ==> valid_file_recovery(file_recovery_new);
+  @ requires valid_header_check_param(buffer, buffer_size, safe_header_only, file_recovery, file_recovery_new);
+  @ ensures  valid_header_check_result(\result, file_recovery_new);
   @ assigns  *file_recovery_new;
   @*/
 static int header_check_ysfc100(const unsigned char *buffer, const unsigned int buffer_size, const unsigned int safe_header_only, const file_recovery_t *file_recovery, file_recovery_t *file_recovery_new)