diff --git a/build-scripts/functions b/build-scripts/functions
index 769b8f55c..325b1c9b0 100644
--- a/build-scripts/functions
+++ b/build-scripts/functions
@@ -796,4 +796,22 @@ log_error() {
     echo "$(basename "$0"): error:" "$@" >&2
 }
 
+# Pin embedded build timestamps so two builds of the same source produce identical binaries.
+# In bootstrap-pr we derive it from core's HEAD commit time and persist it into
+# output/ so downstream jobs (which consume the bootstrap artifacts but no
+# longer have core/.git) can recover the same value.
+if [ -z "$SOURCE_DATE_EPOCH" ]; then
+    if [ -d "$BASEDIR/core/.git" ]; then
+        SOURCE_DATE_EPOCH=$(git -C "$BASEDIR/core" log -1 --format=%ct)
+        mkdir -p "$BASEDIR/output"
+        echo "$SOURCE_DATE_EPOCH" > "$BASEDIR/output/SOURCE_DATE_EPOCH"
+    elif [ -f "$BASEDIR/output/SOURCE_DATE_EPOCH" ]; then
+        SOURCE_DATE_EPOCH=$(cat "$BASEDIR/output/SOURCE_DATE_EPOCH")
+    fi
+    if [ -n "$SOURCE_DATE_EPOCH" ]; then
+        export SOURCE_DATE_EPOCH
+        log_info "SOURCE_DATE_EPOCH=$SOURCE_DATE_EPOCH"
+    fi
+fi
+
 _IS_FUNCTIONS_SOURCED=yes