diff --git a/lib/srfi/160/base.sld b/lib/srfi/160/base.sld
index bce22d49..fb75093e 100644
--- a/lib/srfi/160/base.sld
+++ b/lib/srfi/160/base.sld
@@ -119,7 +119,13 @@
     (define (f64vector . ls) (list->f64vector ls))
     (define (c64vector . ls) (list->c64vector ls))
     (define (c128vector . ls) (list->c128vector ls))
-    (define (make-u1vector len) (make-uvector SEXP_U1 len))
+    (define (make-u1vector len . o)
+      (let ((res (make-uvector SEXP_U1 len)))
+        (if (and (pair? o) (not (zero? (car o))))
+            (do ((i 0 (+ i 1)))
+                ((>= i len))
+              (u1vector-set! res i 1)))
+        res))
     (define make-u8vector make-bytevector)
     (define (make-s8vector len . o)
       (let ((res (make-uvector SEXP_S8 len)))