diff --git a/fs/adfs/adfs.h b/fs/adfs/adfs.h
index a8a58d864f960d89cccd8e25c29f05826f2b290e..718ac1f440c6729c334b800375d853a5bd107366 100644
--- a/fs/adfs/adfs.h
+++ b/fs/adfs/adfs.h
@@ -112,7 +112,7 @@ struct object_info {
 /* RISC OS 12-bit filetype converts to ,xyz hex filename suffix */
 static inline int append_filetype_suffix(char *buf, __u16 filetype)
 {
-	if (filetype == -1)
+	if (filetype == 0xffff)	/* no explicit 12-bit file type was set */
 		return 0;
 
 	*buf++ = ',';