diff --git a/guix/store.scm b/guix/store.scm
index 560e5675ec..4bb2270a59 100644
--- a/guix/store.scm
+++ b/guix/store.scm
@@ -162,7 +162,7 @@
          (l (bytevector-length s))
          (m (modulo l 8))
          (b (make-bytevector (+ 8 l (if (zero? m) 0 (- 8 m))))))
-    (bytevector-u64-native-set! b 0 l)
+    (bytevector-u32-set! b 0 l (endianness little))
     (bytevector-copy! s 0 b 8 l)
     (put-bytevector p b)))