diff --git a/src/file_cab.c b/src/file_cab.c
index 0e9bda47..02328d48 100644
--- a/src/file_cab.c
+++ b/src/file_cab.c
@@ -32,6 +32,7 @@
 #include "common.h"
 #include "filegen.h"
 
+/*@ requires \valid(file_stat); */
 static void register_header_check_cab(file_stat_t *file_stat);
 
 const file_hint_t file_hint_cab= {
@@ -58,14 +59,26 @@ struct cab_header {
   uint16_t number;
 } __attribute__ ((gcc_struct, __packed__));
 
+/*@
+  @ requires buffer_size >= sizeof(struct cab_header) ;
+  @ 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_cab, buffer+(..), file_recovery, file_recovery_new);
+  @ assigns  *file_recovery_new;
+  @ ensures \result == 0 || \result == 1;
+  @ ensures  \result!=0 ==> valid_file_recovery(file_recovery_new);
+  @*/
 static int header_check_cab(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)
 {
   const struct cab_header *cab_hdr=(const struct cab_header*)buffer;
-  if(le16(cab_hdr->cab_version)==0x0103 && le32(cab_hdr->filesize) >= sizeof(struct cab_header))
+  const unsigned int filesize=le32(cab_hdr->filesize);
+  if(le16(cab_hdr->cab_version)==0x0103 && filesize >= sizeof(struct cab_header))
   {
     reset_file_recovery(file_recovery_new);
     file_recovery_new->extension=file_hint_cab.extension;
-    file_recovery_new->calculated_file_size=(uint64_t)le32(cab_hdr->filesize);
+    file_recovery_new->calculated_file_size=filesize;
     file_recovery_new->data_check=&data_check_size;
     file_recovery_new->file_check=&file_check_size;
     return 1;