diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index 7954aa1..bfc2d20 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -533,6 +533,12 @@
 
   # type becomes list<any>
   var somelist = rand() > 0 ? [1, 2, 3] : ['a', 'b', 'c']
+
+  var lines =<< trim END
+    var d = {dd: test_null_list()}
+    d.dd[0] = 0
+  END
+  CheckDefExecFailure(lines, 'E1147:', 2)
 enddef
 
 def Test_assignment_list_vim9script()
@@ -567,12 +573,20 @@
   assert_equal({nest: {this: 123, that: 456}, nr: 0}, anydict)
 
   var lines =<< trim END
-    vim9script
     var dd = {}
     dd.two = 2
     assert_equal({two: 2}, dd)
   END
-  CheckScriptSuccess(lines)
+  CheckDefAndScriptSuccess(lines)
+
+  lines =<< trim END
+    var d = {dd: {}}
+    d.dd[0] = 2
+    d.dd['x'] = 3
+    d.dd.y = 4
+    assert_equal({dd: {0: 2, x: 3, y: 4}}, d)
+  END
+  CheckDefAndScriptSuccess(lines)
 
   lines =<< trim END
     var dd = {one: 1}
@@ -641,6 +655,18 @@
     assert_equal({a: 43}, FillDict())
   END
   CheckScriptSuccess(lines)
+
+  lines =<< trim END
+    var d = {dd: test_null_dict()}
+    d.dd[0] = 0
+  END
+  CheckDefExecFailure(lines, 'E1103:', 2)
+
+  lines =<< trim END
+    var d = {dd: 'string'}
+    d.dd[0] = 0
+  END
+  CheckDefExecFailure(lines, 'E1148:', 2)
 enddef
 
 def Test_assignment_local()
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index d936bc2..7f88cfa 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -276,6 +276,30 @@
         res)
 enddef
 
+def s:ScriptFuncStoreIndex()
+  var d = {dd: {}}
+  d.dd[0] = 0
+enddef
+
+def Test_disassemble_store_index()
+  var res = execute('disass s:ScriptFuncStoreIndex')
+  assert_match('<SNR>\d*_ScriptFuncStoreIndex\_s*' ..
+        'var d = {dd: {}}\_s*' ..
+        '\d PUSHS "dd"\_s*' ..
+        '\d NEWDICT size 0\_s*' ..
+        '\d NEWDICT size 1\_s*' ..
+        '\d STORE $0\_s*' ..
+        'd.dd\[0\] = 0\_s*' ..
+        '\d PUSHNR 0\_s*' ..
+        '\d PUSHNR 0\_s*' ..
+        '\d LOAD $0\_s*' ..
+        '\d MEMBER dd\_s*' ..
+        '\d STOREINDEX\_s*' ..
+        '\d\+ PUSHNR 0\_s*' ..
+        '\d\+ RETURN',
+        res)
+enddef
+
 def s:ListAssign()
   var x: string
   var y: string