diff --git a/src/eval.c b/src/eval.c
index 0bb1882..3cd73b6 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -2882,6 +2882,12 @@
 	di = find_var(lp->ll_name, NULL, TRUE);
 	if (di == NULL)
 	    ret = FAIL;
+	else if ((di->di_flags & DI_FLAGS_FIX)
+			&& di->di_tv.v_type != VAR_DICT
+			&& di->di_tv.v_type != VAR_LIST)
+	    /* For historic reasons this error is not given for a list or dict.
+	     * E.g., the b: dict could be locked/unlocked. */
+	    EMSG2(_("E940: Cannot lock or unlock variable %s"), lp->ll_name);
 	else
 	{
 	    if (lock)
diff --git a/src/testdir/test_changedtick.vim b/src/testdir/test_changedtick.vim
index f273f0f..9aaba27 100644
--- a/src/testdir/test_changedtick.vim
+++ b/src/testdir/test_changedtick.vim
@@ -33,13 +33,19 @@
 endfunc
 
 func Test_changedtick_fixed()
-  call assert_fails('let b:changedtick = 4', 'E46')
-  call assert_fails('let b:["changedtick"] = 4', 'E46')
+  call assert_fails('let b:changedtick = 4', 'E46:')
+  call assert_fails('let b:["changedtick"] = 4', 'E46:')
 
-  call assert_fails('unlet b:changedtick', 'E795')
-  call assert_fails('unlet b:["changedtick"]', 'E46')
+  call assert_fails('lockvar b:changedtick', 'E940:')
+  call assert_fails('lockvar b:["changedtick"]', 'E46:')
+  call assert_fails('unlockvar b:changedtick', 'E940:')
+  call assert_fails('unlockvar b:["changedtick"]', 'E46:')
+  call assert_fails('unlet b:changedtick', 'E795:')
+  call assert_fails('unlet b:["changedtick"]', 'E46:')
 
   let d = b:
-  call assert_fails('unlet d["changedtick"]', 'E46')
+  call assert_fails('lockvar d["changedtick"]', 'E46:')
+  call assert_fails('unlockvar d["changedtick"]', 'E46:')
+  call assert_fails('unlet d["changedtick"]', 'E46:')
 
 endfunc
diff --git a/src/version.c b/src/version.c
index c1dff6c..5db4b11 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    343,
+/**/
     342,
 /**/
     341,