diff --git a/scripts/package-codex-plugin.sh b/scripts/package-codex-plugin.sh
index 00399f061b..2594fc10f6 100755
--- a/scripts/package-codex-plugin.sh
+++ b/scripts/package-codex-plugin.sh
@@ -294,7 +294,7 @@ case "$FORMAT" in
     (
       cd "$STAGE"
       rm -f "$OUTPUT"
-      COPYFILE_DISABLE=1 zip -X -q - -@ <"$ARCHIVE_LIST" >"$OUTPUT"
+      COPYFILE_DISABLE=1 TZ=UTC zip -X -q - -@ <"$ARCHIVE_LIST" >"$OUTPUT"
     )
     ;;
   tar.gz)
diff --git a/tests/codex/test-package-codex-plugin.sh b/tests/codex/test-package-codex-plugin.sh
index 62c73f1cc1..f3faab9602 100755
--- a/tests/codex/test-package-codex-plugin.sh
+++ b/tests/codex/test-package-codex-plugin.sh
@@ -135,6 +135,8 @@ echo "Codex package archive tests"
 
 metadata_source="$TEST_ROOT/metadata-source"
 archive="$TEST_ROOT/superpowers"
+utc_archive="$TEST_ROOT/superpowers-utc.zip"
+seoul_archive="$TEST_ROOT/superpowers-seoul.zip"
 tar_archive="$TEST_ROOT/superpowers.tar.gz"
 extracted="$TEST_ROOT/extracted"
 tar_extracted="$TEST_ROOT/tar-extracted"
@@ -160,6 +162,26 @@ assert_contains "$output" "Archive:" "reports archive path"
 assert_contains "$output" "Format:  zip" "reports default zip format"
 assert_contains "$output" "SHA-256:" "reports archive checksum"
 
+if output="$(TZ=UTC "$SCRIPT_UNDER_TEST" --allow-dirty --metadata-source "$metadata_source" --output "$utc_archive" 2>&1)"; then
+  pass "package script writes ZIP archive under UTC"
+else
+  fail "package script writes ZIP archive under UTC"
+  printf '%s\n' "$output" | sed 's/^/      /'
+fi
+
+if output="$(TZ=Asia/Seoul "$SCRIPT_UNDER_TEST" --allow-dirty --metadata-source "$metadata_source" --output "$seoul_archive" 2>&1)"; then
+  pass "package script writes ZIP archive under Asia/Seoul"
+else
+  fail "package script writes ZIP archive under Asia/Seoul"
+  printf '%s\n' "$output" | sed 's/^/      /'
+fi
+
+if cmp -s "$utc_archive" "$seoul_archive"; then
+  pass "ZIP archives are byte-identical across time zones"
+else
+  fail "ZIP archives are byte-identical across time zones"
+fi
+
 extract_archive "$archive" "$extracted"
 
 archive_paths="$(list_archive "$archive" | normalize_archive_paths)"
@@ -210,8 +232,15 @@ assert_equals "$tar_archive_paths" "$archive_paths" "zip and tar.gz archives con
 tar_task_brief_mode="$(tar -tzvf "$tar_archive" skills/subagent-driven-development/scripts/task-brief | awk '{print $1}')"
 assert_equals "$tar_task_brief_mode" "-rwxr-xr-x" "tar.gz archive preserves executable script mode"
 
-tar_metadata_times="$(tar -tzvf "$tar_archive" | awk '{print $6, $7, $8}' | sort -u)"
-assert_equals "$tar_metadata_times" "Dec 31 1969" "tar.gz archive normalizes entry timestamps"
+tar_metadata_times="$(python3 - "$tar_archive" <<'PY'
+import sys
+import tarfile
+
+with tarfile.open(sys.argv[1]) as archive:
+    print("\n".join(sorted({str(member.mtime) for member in archive.getmembers()})))
+PY
+)"
+assert_equals "$tar_metadata_times" "0" "tar.gz archive normalizes entry timestamps"
 
 metadata_archive="$TEST_ROOT/metadata-source.tar.gz"
 metadata_zip="$TEST_ROOT/metadata-source.zip"