diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index 05a3cd6..f87e920 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -1059,7 +1059,7 @@
   call CheckDefFailure(["CallMe2('yes' , 'no')"], 'E1068:')
 
   call CheckDefFailure(["v:nosuch += 3"], 'E1001:')
-  call CheckDefFailure(["let v:statusmsg = ''"], 'E1064:')
+  call CheckDefFailure(["let v:statusmsg = ''"], 'E1016: Cannot declare a v: variable:')
   call CheckDefFailure(["let asdf = v:nosuch"], 'E1001:')
 
   call CheckDefFailure(["echo len('asdf'"], 'E110:')
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index ec1fc87..a733bf1 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -322,15 +322,15 @@
   call CheckDefFailure(['let &option'], 'E1052:')
   call CheckDefFailure(['&g:option = 5'], 'E113:')
 
-  call CheckDefFailure(['let $VAR = 5'], 'E1065:')
+  call CheckDefFailure(['let $VAR = 5'], 'E1016: Cannot declare an environment variable:')
 
   call CheckDefFailure(['let @~ = 5'], 'E354:')
   call CheckDefFailure(['let @a = 5'], 'E1066:')
 
-  call CheckDefFailure(['let g:var = 5'], 'E1016:')
-  call CheckDefFailure(['let w:var = 5'], 'E1079:')
-  call CheckDefFailure(['let b:var = 5'], 'E1078:')
-  call CheckDefFailure(['let t:var = 5'], 'E1080:')
+  call CheckDefFailure(['let g:var = 5'], 'E1016: Cannot declare a global variable:')
+  call CheckDefFailure(['let w:var = 5'], 'E1016: Cannot declare a window variable:')
+  call CheckDefFailure(['let b:var = 5'], 'E1016: Cannot declare a buffer variable:')
+  call CheckDefFailure(['let t:var = 5'], 'E1016: Cannot declare a tab variable:')
 
   call CheckDefFailure(['let anr = 4', 'anr ..= "text"'], 'E1019:')
   call CheckDefFailure(['let xnr += 4'], 'E1020:')
@@ -1812,14 +1812,41 @@
   CheckScriptSuccess([
       'vim9script',
       'g:var = 123',
-      'let w:var = 777',
+      'b:var = 456',
+      'w:var = 777',
+      't:var = 888',
       'unlet g:var w:var # something',
       ])
 
   CheckScriptFailure([
       'vim9script',
       'let g:var = 123',
-      ], 'E1016:')
+      ], 'E1016: Cannot declare a global variable:')
+
+  CheckScriptFailure([
+      'vim9script',
+      'let b:var = 123',
+      ], 'E1016: Cannot declare a buffer variable:')
+
+  CheckScriptFailure([
+      'vim9script',
+      'let w:var = 123',
+      ], 'E1016: Cannot declare a window variable:')
+
+  CheckScriptFailure([
+      'vim9script',
+      'let t:var = 123',
+      ], 'E1016: Cannot declare a tab variable:')
+
+  CheckScriptFailure([
+      'vim9script',
+      'let v:version = 123',
+      ], 'E1016: Cannot declare a v: variable:')
+
+  CheckScriptFailure([
+      'vim9script',
+      'let $VARIABLE = "text"',
+      ], 'E1016: Cannot declare an environment variable:')
 
   CheckScriptFailure([
       'vim9script',