Closes #15432: GzipFile mtime argument was added in 2.7.
diff --git a/Doc/library/gzip.rst b/Doc/library/gzip.rst
index aa89c2c..e26fe28 100644
--- a/Doc/library/gzip.rst
+++ b/Doc/library/gzip.rst
@@ -77,6 +77,9 @@
    .. versionchanged:: 2.7
       Support for zero-padded files was added.
 
+   .. versionadded:: 2.7
+      The *mtime* argument.
+
 
 .. function:: open(filename[, mode[, compresslevel]])