diff --git a/t/t5301-sliding-window.sh b/t/t5301-sliding-window.sh
index a6dbb04a86..fce77f1255 100755
--- a/t/t5301-sliding-window.sh
+++ b/t/t5301-sliding-window.sh
@@ -12,7 +12,7 @@ test_expect_success \
      for i in a b c
      do
          echo $i >$i &&
-         dd if=/dev/urandom bs=32k count=1 >>$i &&
+         test-genrandom "$i" 32768 >>$i &&
          git-update-index --add $i || return 1
      done &&
      echo d >d && cat c >>d && git-update-index --add d &&