diff --git a/third_party/linux/def.bzl b/third_party/linux/def.bzl
index 1ce6170..1f16d2e 100644
--- a/third_party/linux/def.bzl
+++ b/third_party/linux/def.bzl
@@ -118,7 +118,7 @@
             export BISON_PKGDATADIR=$(realpath $(dirname $BISON)/../share/bison)
             builddir=$(mktemp -d)
             # All source files have the same timestamp, take it from an arbitrary file.
-            build_timestamp=$(date -r {kernel_src}/README)
+            build_timestamp=$(date --utc -r {kernel_src}/README)
 
             mkdir {kernel_src}/.bin
             cp {kconfig} $builddir/.config