python · serhiy-storchaka · May 22, 2026 · May 22, 2026
diff --git a/Doc/library/gzip.rst b/Doc/library/gzip.rst
@@ -108,9 +108,13 @@ The module defines the following items:
    is no compression. The default is ``9``.
 
    The optional *mtime* argument is the timestamp requested by gzip. The time
-   is in Unix format, i.e., seconds since 00:00:00 UTC, January 1, 1970.
-   If *mtime* is omitted or ``None``, the current time is used. Use *mtime* = 0
-   to generate a compressed stream that does not depend on creation time.
+   is in Unix format, i.e., seconds since 00:00:00 UTC, January 1, 1970. Set
+   *mtime* to ``0`` to generate a compressed stream that does not depend on
+   creation time. If *mtime* is omitted or ``None``, the current time is used;
+   however, if the current time is outside the range 00:00:00 UTC, January 1,
+   1970 through 06:28:15 UTC, February 7, 2106, or explicitly passed *mtime*
+   argument is outside the range ``0`` to ``2**32-1``, then the value ``0``
+   is used instead.
 
    See below for the :attr:`mtime` attribute that is set when decompressing.
 

diff --git a/Lib/gzip.py b/Lib/gzip.py
@@ -188,8 +188,10 @@ def __init__(self, filename=None, mode=None,
 
         The optional mtime argument is the timestamp requested by gzip. The time
         is in Unix format, i.e., seconds since 00:00:00 UTC, January 1, 1970.
-        If mtime is omitted or None, the current time is used. Use mtime = 0
-        to generate a compressed stream that does not depend on creation time.
+        Set mtime to 0 to generate a compressed stream that does not depend on
+        creation time. If mtime is omitted or None, the current time is used.
+        If the resulting mtime is outside the range 0 to 2**32-1, then the
+        value 0 is used instead.
 
         """
 
@@ -295,6 +297,8 @@ def _write_gzip_header(self, compresslevel):
         mtime = self._write_mtime
         if mtime is None:
             mtime = time.time()
+        if not 0 <= mtime < 2**32:
+            mtime = 0
         write32u(self.fileobj, int(mtime))
         if compresslevel == _COMPRESS_LEVEL_BEST:
             xfl = b'\002'
@@ -663,6 +667,8 @@ def compress(data, compresslevel=_COMPRESS_LEVEL_TRADEOFF, *, mtime=0):
     gzip_data = zlib.compress(data, level=compresslevel, wbits=31)
     if mtime is None:
         mtime = time.time()
+    if not 0 <= mtime < 2**32:
+        mtime = 0
     # Reuse gzip header created by zlib, replace mtime and OS byte for
     # consistency.
     header = struct.pack("<4sLBB", gzip_data, int(mtime), gzip_data[8], 255)

diff --git a/Lib/test/test_gzip.py b/Lib/test/test_gzip.py
@@ -10,6 +10,7 @@
 import sys
 import unittest
 from subprocess import PIPE, Popen
+from unittest import mock
 from test.support import catch_unraisable_exception
 from test.support import force_not_colorized_test_class, import_helper
 from test.support import os_helper
@@ -350,6 +351,26 @@ def test_mtime(self):
             self.assertEqual(dataRead, data1)
             self.assertEqual(fRead.mtime, mtime)
 
+    def test_mtime_out_of_range(self):
+        for mtime in (-1, 2**32):
+            with gzip.GzipFile(self.filename, 'w', mtime=mtime) as fWrite:
+                fWrite.write(data1)
+            with gzip.GzipFile(self.filename) as fRead:
+                fRead.read(1)
+                self.assertEqual(fRead.mtime, 0)
+            datac = gzip.compress(data1, mtime=mtime)
+            with gzip.GzipFile(fileobj=io.BytesIO(datac)) as fRead:
+                fRead.read(1)
+                self.assertEqual(fRead.mtime, 0)
+
+        for mtime in (-1, 2**32):
+            with mock.patch('time.time', return_value=float(mtime)):
+                with gzip.GzipFile(self.filename, 'w') as fWrite:
+                    fWrite.write(data1)
+                with gzip.GzipFile(self.filename) as fRead:
+                    fRead.read(1)
+                    self.assertEqual(fRead.mtime, 0)
+
     def test_metadata(self):
         mtime = 123456789
 

diff --git a/Misc/NEWS.d/next/Library/2025-05-19-20-29-35.gh-issue-133998.KmElUw.rst b/Misc/NEWS.d/next/Library/2025-05-19-20-29-35.gh-issue-133998.KmElUw.rst
@@ -0,0 +1,5 @@
+Fix :exc:`struct.error` exception when creating a file with
+:class:`gzip.GzipFile` or compressing data with :func:`gzip.compress`
+if the system time is outside the range 00:00:00 UTC, January 1, 1970
+through 06:28:15 UTC, February 7, 2106, or explicitly passed *mtime*
+argument is outside the range ``0`` to ``2**32-1``.