diff --git a/src/testdir/test_blob.vim b/src/testdir/test_blob.vim
index a29e2e6..4b6774f 100644
--- a/src/testdir/test_blob.vim
+++ b/src/testdir/test_blob.vim
@@ -207,6 +207,7 @@
   call assert_equal(0z001122, b)
   call add(b, '51')
   call assert_equal(0z00112233, b)
+  call assert_equal(1, add(test_null_blob(), 0x22))
 
   call assert_fails('call add(b, [9])', 'E745:')
   call assert_fails('call add("", 0x01)', 'E897:')