diff --git a/src/io.c b/src/io.c
index c4224c84..8ae03c1c 100644
--- a/src/io.c
+++ b/src/io.c
@@ -89,7 +89,7 @@ int Read_byte_line(FILE *file, char *line, size_t size)
 }
 // Ecrit des octets
 // Renvoie -1 si OK, 0 en cas d'erreur
-int Write_bytes(FILE *file, void *src, size_t size)
+int Write_bytes(FILE *file, const void *src, size_t size)
 {
   return fwrite(src, 1, size, file) == size;
 }
diff --git a/src/io.h b/src/io.h
index 0e74ef85..d2163532 100644
--- a/src/io.h
+++ b/src/io.h
@@ -51,7 +51,7 @@ int Read_bytes(FILE *file, void *dest, size_t size);
 // Read a line from an open file. Returns true if OK, false in case of error
 int Read_byte_line(FILE *file, char *line, size_t size);
 /// Writes several bytes to an open file. Returns true if OK, false if a file i/o error occurred.
-int Write_bytes(FILE *file, void *dest, size_t size);
+int Write_bytes(FILE *file, const void *dest, size_t size);
 
 /// Reads a 16-bit Low-Endian word from an open file. Returns true if OK, false if a file i/o error occurred.
 int Read_word_le(FILE *file, word *dest);
@@ -156,4 +156,4 @@ int Remove_path(const char * path);
 /// Remove the directory
 int Remove_directory(const char * path);
 
-#endif
\ No newline at end of file
+#endif