diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index bf3e889..e31e2ed 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -4311,6 +4311,10 @@
     call assert_equal(["🁰🁳"], blob2str(0zF09F81B0.F09F81B3))
     call assert_equal(['«»'], blob2str(0zABBB, {'encoding': 'latin1'}))
     call assert_equal(['«»'], blob2str(0zC2ABC2BB, {'encoding': 'utf8'}))
+    call assert_equal(['«»'], blob2str(0zC2ABC2BB, {'encoding': 'utf-8'}))
+
+    call assert_equal(['a'], blob2str(0z61, test_null_dict()))
+    call assert_equal(['a'], blob2str(0z61, {'encoding': test_null_string()}))
 
     #" Invalid encoding
     call assert_fails("call blob2str(0z80)", "E1515: Unable to convert from 'utf-8' encoding")