diff --git a/pkgs/racket-doc/file/scribblings/gzip.scrbl b/pkgs/racket-doc/file/scribblings/gzip.scrbl
index 9aa4d90f59..01e92e5cf8 100644
--- a/pkgs/racket-doc/file/scribblings/gzip.scrbl
+++ b/pkgs/racket-doc/file/scribblings/gzip.scrbl
@@ -8,13 +8,17 @@ utilities to create archive files in @exec{gzip} format, or simply to
 compress data using the @exec{pkzip} ``deflate'' method.}
 
 @defproc[(gzip [in-file path-string?]
-               [out-file path-string? (string-append in-file ".gz")])
+               [out-file path-string? (path-add-extension in-file ".gz" #".")])
          void?]{
 
 Compresses data to the same format as the @exec{gzip} utility, writing
 the compressed data directly to a file. The @racket[in-file] argument
 is the name of the file to compress. If the file named by
-@racket[out-file] exists, it will be overwritten.}
+@racket[out-file] exists, it will be overwritten.
+
+@history[#:changed "6.8.0.2"
+         @elem{Changed default expression of @racket[out-file] to use
+               @racket[path-add-extension] instead of @racket[string-append].}]}
 
 
 @defproc[(gzip-through-ports [in input-port?]
diff --git a/racket/collects/file/gzip.rkt b/racket/collects/file/gzip.rkt
index a926ae09ea..0429c5923e 100644
--- a/racket/collects/file/gzip.rkt
+++ b/racket/collects/file/gzip.rkt
@@ -2208,7 +2208,7 @@
 
 (define gzip
   (case-lambda
-   [(infile) (gzip infile (string-append infile ".gz"))]
+   [(infile) (gzip infile (path-add-extension infile ".gz" #"."))]
    [(infile outfile) ((car (code)) infile outfile)]))
 
 (define (gzip-through-ports in out origname time_stamp)