diff --git a/stdlib/filename.mli b/stdlib/filename.mli
index d7452168c..e3b2b7c7f 100644
--- a/stdlib/filename.mli
+++ b/stdlib/filename.mli
@@ -76,9 +76,8 @@ val temp_file : string -> string -> string
    Under Unix, the temporary directory is [/tmp] by default; if set,
    the value of the environment variable [TMPDIR] is used instead.
    Under Windows, the name of the temporary directory is the
-   value of the environment variable [TEMP],
-   or [C:\temp] by default.
-   Under MacOS, the name of the temporary directory is given
+   value of the environment variable [TEMP], or [C:\temp] by default.
+   Under MacOS 9, the name of the temporary directory is given
    by the environment variable [TempFolder]; if not set,
    temporary files are created in the current directory. *)
 
diff --git a/stdlib/lexing.mli b/stdlib/lexing.mli
index c99380cfb..7896abb66 100644
--- a/stdlib/lexing.mli
+++ b/stdlib/lexing.mli
@@ -24,14 +24,17 @@ type position = {
   pos_cnum : int;
 }
 (** A value of type [position] describes a point in a source file.
-    [pos_fname] is the file name; [pos_lnum] is the line number;
-    [pos_bol] is the number of characters between the beginning of the
-    lexbuf and the beginning of the line; [pos_cnum] is offset of the
-    position from the beginning of the file.
+   [pos_fname] is the file name; [pos_lnum] is the line number;
+   [pos_bol] is the offset of the beginning of the line (number
+   of characters between the beginning of the file and the beginning
+   of the line); [pos_cnum] is the offset of the position (number of
+   characters between the beginning of the file and the position).
  *)
 
 val dummy_pos : position;;
-(** An arbitrary value of type [position]. *)
+(** A value of type [position], guaranteed to be different from any
+   valid position.
+ *)
 
 
 (** {6 Lexer buffers} *)