diff --git a/src/testdir/test_blob.vim b/src/testdir/test_blob.vim
index b41ca78..d56c4f7 100644
--- a/src/testdir/test_blob.vim
+++ b/src/testdir/test_blob.vim
@@ -428,6 +428,23 @@
       call remove(test_null_blob(), 1, 2)
   END
   call CheckLegacyAndVim9Failure(lines, 'E979:')
+
+  let lines =<< trim END
+      let b = 0zDEADBEEF
+      lockvar b
+      call remove(b, 0)
+      unlockvar b
+  END
+  call CheckScriptFailure(lines, 'E741:')
+
+  " can only check at script level, not in a :def function
+  let lines =<< trim END
+      vim9script
+      var b = 0zDEADBEEF
+      lockvar b
+      remove(b, 0)
+  END
+  call CheckScriptFailure(lines, 'E741:')
 endfunc
 
 func Test_blob_read_write()
@@ -543,6 +560,22 @@
       insert(test_null_blob(), 0x33)
   END
   call CheckDefExecAndScriptFailure(lines, 'E1131:')
+
+  let lines =<< trim END
+      let b = 0zDEADBEEF
+      lockvar b
+      call insert(b, 3)
+      unlockvar b
+  END
+  call CheckScriptFailure(lines, 'E741:')
+
+  let lines =<< trim END
+      vim9script
+      var b = 0zDEADBEEF
+      lockvar b
+      insert(b, 3)
+  END
+  call CheckScriptFailure(lines, 'E741:')
 endfunc
 
 func Test_blob_reverse()