diff --git a/src/dosfs.c b/src/dosfs.c
index cebdd0d..e295be4 100644
--- a/src/dosfs.c
+++ b/src/dosfs.c
@@ -243,7 +243,7 @@ read_fat_chain(dosfs_t *fsd, unsigned int first, int *length)
  * offset, i.e. one that can be used with lseek()/pread().
  */
 int
-get_byte_offset(dosfs_t *fsd, dosfile_t *file, int f_offset)
+get_byte_offset(dosfs_t *fsd, dosfile_t *file, unsigned int f_offset)
 {
     int coff, csz;
 
diff --git a/src/dosfs.h b/src/dosfs.h
index d422818..500d9df 100644
--- a/src/dosfs.h
+++ b/src/dosfs.h
@@ -80,6 +80,6 @@ void close_image(dosfs_t *);
 dosfile_t *dos_listdir(dosfs_t *, unsigned int);
 void dos_freedir(dosfile_t *);
 
-int get_byte_offset(dosfs_t *, dosfile_t *, int);
+int get_byte_offset(dosfs_t *, dosfile_t *, unsigned int);
 
 #endif /* !_FAT12_H */