diff --git a/src/testdir/test_blob.vim b/src/testdir/test_blob.vim
index 3ce9575..69c8696 100644
--- a/src/testdir/test_blob.vim
+++ b/src/testdir/test_blob.vim
@@ -37,6 +37,7 @@
       call assert_fails('VAR b = 0z001122.')
       call assert_fails('call get("", 1)', 'E896:')
       call assert_equal(0, len(test_null_blob()))
+      call assert_equal(0z, copy(test_null_blob()))
   END
   call CheckLegacyAndVim9Success(lines)
 endfunc
@@ -369,6 +370,14 @@
       add(test_null_blob(), 0x22)
   END
   call CheckDefExecAndScriptFailure(lines, 'E1131:')
+
+  let lines =<< trim END
+      let b = 0zDEADBEEF
+      lockvar b
+      call add(b, 0)
+      unlockvar b
+  END
+  call CheckScriptFailure(lines, 'E741:')
 endfunc
 
 func Test_blob_empty()
@@ -445,6 +454,9 @@
       remove(b, 0)
   END
   call CheckScriptFailure(lines, 'E741:')
+
+  call assert_fails('echo remove(0z1020, [])', 'E745:')
+  call assert_fails('echo remove(0z1020, 0, [])', 'E745:')
 endfunc
 
 func Test_blob_read_write()
@@ -474,6 +486,7 @@
       call assert_equal(0zADEF, filter(0zDEADBEEF, 'v:key % 2'))
   END
   call CheckLegacyAndVim9Success(lines)
+  call assert_fails('echo filter(0z10, "a10")', 'E121:')
 endfunc
 
 " map() item in blob
@@ -489,6 +502,7 @@
       call map(0z00, '[9]')
   END
   call CheckLegacyAndVim9Failure(lines, 'E978:')
+  call assert_fails('echo map(0z10, "a10")', 'E121:')
 endfunc
 
 func Test_blob_index()