diff --git a/src/dict.c b/src/dict.c
index 91c6e55..0bb9dfa 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -758,8 +758,8 @@
 	    }
 	    else if (*action == 'f' && HI2DI(hi2) != di1)
 	    {
-		if (tv_check_lock(di1->di_tv.v_lock, arg_errmsg, TRUE)
-		      || var_check_ro(di1->di_flags, arg_errmsg, TRUE))
+		if (var_check_lock(di1->di_tv.v_lock, arg_errmsg, TRUE)
+			|| var_check_ro(di1->di_flags, arg_errmsg, TRUE))
 		    break;
 		clear_tv(&di1->di_tv);
 		copy_tv(&HI2DI(hi2)->di_tv, &di1->di_tv);
diff --git a/src/eval.c b/src/eval.c
index c30c5d8..484f9bc 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -247,6 +247,7 @@
 static void delete_var(hashtab_T *ht, hashitem_T *hi);
 static void list_one_var(dictitem_T *v, char *prefix, int *first);
 static void list_one_var_a(char *prefix, char_u *name, int type, char_u *string, int *first);
+static int tv_check_lock(typval_T *tv, char_u *name, int use_gettext);
 static char_u *find_option_end(char_u **arg, int *opt_flags);
 
 /* for VIM_VERSION_ defines */
@@ -2332,9 +2333,8 @@
 					     &tv, &di, TRUE, FALSE) == OK)
 	    {
 		if ((di == NULL
-		       || (!var_check_ro(di->di_flags, lp->ll_name, FALSE)
-			  && !tv_check_lock(di->di_tv.v_lock, lp->ll_name,
-								  FALSE)))
+			 || (!var_check_ro(di->di_flags, lp->ll_name, FALSE)
+			   && !tv_check_lock(&di->di_tv, lp->ll_name, FALSE)))
 			&& tv_op(&tv, rettv, op) == OK)
 		    set_var(lp->ll_name, &tv, FALSE);
 		clear_tv(&tv);
@@ -2344,7 +2344,7 @@
 	    set_var(lp->ll_name, rettv, copy);
 	*endp = cc;
     }
-    else if (tv_check_lock(lp->ll_newkey == NULL
+    else if (var_check_lock(lp->ll_newkey == NULL
 		? lp->ll_tv->v_lock
 		: lp->ll_tv->vval.v_dict->dv_lock, lp->ll_name, FALSE))
 	;
@@ -2358,7 +2358,7 @@
 	 */
 	for (ri = rettv->vval.v_list->lv_first; ri != NULL && ll_li != NULL; )
 	{
-	    if (tv_check_lock(ll_li->li_tv.v_lock, lp->ll_name, FALSE))
+	    if (var_check_lock(ll_li->li_tv.v_lock, lp->ll_name, FALSE))
 		return;
 	    ri = ri->li_next;
 	    if (ri == NULL || (!lp->ll_empty2 && lp->ll_n2 == ll_n1))
@@ -2951,9 +2951,9 @@
 	*name_end = cc;
     }
     else if ((lp->ll_list != NULL
-		   && tv_check_lock(lp->ll_list->lv_lock, lp->ll_name, FALSE))
+		 && var_check_lock(lp->ll_list->lv_lock, lp->ll_name, FALSE))
 	    || (lp->ll_dict != NULL
-		  && tv_check_lock(lp->ll_dict->dv_lock, lp->ll_name, FALSE)))
+		 && var_check_lock(lp->ll_dict->dv_lock, lp->ll_name, FALSE)))
 	return FAIL;
     else if (lp->ll_range)
     {
@@ -2964,7 +2964,7 @@
 	while (ll_li != NULL && (lp->ll_empty2 || lp->ll_n2 >= ll_n1))
 	{
 	    li = ll_li->li_next;
-	    if (tv_check_lock(ll_li->li_tv.v_lock, lp->ll_name, FALSE))
+	    if (var_check_lock(ll_li->li_tv.v_lock, lp->ll_name, FALSE))
 		return FAIL;
 	    ll_li = li;
 	    ++ll_n1;
@@ -3034,7 +3034,7 @@
 	    di = HI2DI(hi);
 	    if (var_check_fixed(di->di_flags, name, FALSE)
 		    || var_check_ro(di->di_flags, name, FALSE)
-		    || tv_check_lock(d->dv_lock, name, FALSE))
+		    || var_check_lock(d->dv_lock, name, FALSE))
 		return FAIL;
 
 	    delete_var(ht, hi);
@@ -7866,7 +7866,7 @@
     {
 	/* existing variable, need to clear the value */
 	if (var_check_ro(v->di_flags, name, FALSE)
-			       || tv_check_lock(v->di_tv.v_lock, name, FALSE))
+			      || var_check_lock(v->di_tv.v_lock, name, FALSE))
 	    return;
 
 	/*
@@ -8021,31 +8021,12 @@
 }
 
 /*
- * Check if a variable name is valid.
- * Return FALSE and give an error if not.
- */
-    int
-valid_varname(char_u *varname)
-{
-    char_u *p;
-
-    for (p = varname; *p != NUL; ++p)
-	if (!eval_isnamec1(*p) && (p == varname || !VIM_ISDIGIT(*p))
-						   && *p != AUTOLOAD_CHAR)
-	{
-	    semsg(_(e_illvar), varname);
-	    return FALSE;
-	}
-    return TRUE;
-}
-
-/*
- * Return TRUE if typeval "tv" is set to be locked (immutable).
+ * Return TRUE if "flags" indicates variable "name" is locked (immutable).
  * Also give an error message, using "name" or _("name") when use_gettext is
  * TRUE.
  */
     int
-tv_check_lock(int lock, char_u *name, int use_gettext)
+var_check_lock(int lock, char_u *name, int use_gettext)
 {
     if (lock & VAR_LOCKED)
     {
@@ -8067,6 +8048,56 @@
 }
 
 /*
+ * Return TRUE if typeval "tv" and its value are set to be locked (immutable).
+ * Also give an error message, using "name" or _("name") when use_gettext is
+ * TRUE.
+ */
+    static int
+tv_check_lock(typval_T *tv, char_u *name, int use_gettext)
+{
+    int	lock = 0;
+
+    switch (tv->v_type)
+    {
+	case VAR_BLOB:
+	    if (tv->vval.v_blob != NULL)
+		lock = tv->vval.v_blob->bv_lock;
+	    break;
+	case VAR_LIST:
+	    if (tv->vval.v_list != NULL)
+		lock = tv->vval.v_list->lv_lock;
+	    break;
+	case VAR_DICT:
+	    if (tv->vval.v_dict != NULL)
+		lock = tv->vval.v_dict->dv_lock;
+	    break;
+	default:
+	    break;
+    }
+    return var_check_lock(tv->v_lock, name, use_gettext)
+		    || (lock != 0 && var_check_lock(lock, name, use_gettext));
+}
+
+/*
+ * Check if a variable name is valid.
+ * Return FALSE and give an error if not.
+ */
+    int
+valid_varname(char_u *varname)
+{
+    char_u *p;
+
+    for (p = varname; *p != NUL; ++p)
+	if (!eval_isnamec1(*p) && (p == varname || !VIM_ISDIGIT(*p))
+						   && *p != AUTOLOAD_CHAR)
+	{
+	    semsg(_(e_illvar), varname);
+	    return FALSE;
+	}
+    return TRUE;
+}
+
+/*
  * Copy the values from typval_T "from" to typval_T "to".
  * When needed allocates string or increases reference count.
  * Does not make a copy of a list, blob or dict but copies the reference!
@@ -10711,13 +10742,13 @@
     else if (argvars[0].v_type == VAR_LIST)
     {
 	if ((l = argvars[0].vval.v_list) == NULL
-	      || (!map && tv_check_lock(l->lv_lock, arg_errmsg, TRUE)))
+	      || (!map && var_check_lock(l->lv_lock, arg_errmsg, TRUE)))
 	    return;
     }
     else if (argvars[0].v_type == VAR_DICT)
     {
 	if ((d = argvars[0].vval.v_dict) == NULL
-	      || (!map && tv_check_lock(d->dv_lock, arg_errmsg, TRUE)))
+	      || (!map && var_check_lock(d->dv_lock, arg_errmsg, TRUE)))
 	    return;
     }
     else
@@ -10755,9 +10786,10 @@
 
 		    --todo;
 		    di = HI2DI(hi);
-		    if (map &&
-			    (tv_check_lock(di->di_tv.v_lock, arg_errmsg, TRUE)
-			    || var_check_ro(di->di_flags, arg_errmsg, TRUE)))
+		    if (map && (var_check_lock(di->di_tv.v_lock,
+							   arg_errmsg, TRUE)
+				|| var_check_ro(di->di_flags,
+							   arg_errmsg, TRUE)))
 			break;
 		    vimvars[VV_KEY].vv_str = vim_strsave(di->di_key);
 		    r = filter_map_one(&di->di_tv, expr, map, &rem);
@@ -10813,7 +10845,7 @@
 
 	    for (li = l->lv_first; li != NULL; li = nli)
 	    {
-		if (map && tv_check_lock(li->li_tv.v_lock, arg_errmsg, TRUE))
+		if (map && var_check_lock(li->li_tv.v_lock, arg_errmsg, TRUE))
 		    break;
 		nli = li->li_next;
 		vimvars[VV_KEY].vv_nr = idx;
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 4c03470..6982ddf 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -1248,7 +1248,7 @@
     if (argvars[0].v_type == VAR_LIST)
     {
 	if ((l = argvars[0].vval.v_list) != NULL
-		&& !tv_check_lock(l->lv_lock,
+		&& !var_check_lock(l->lv_lock,
 					 (char_u *)N_("add() argument"), TRUE)
 		&& list_append_tv(l, &argvars[1]) == OK)
 	    copy_tv(&argvars[0], rettv);
@@ -1256,7 +1256,7 @@
     else if (argvars[0].v_type == VAR_BLOB)
     {
 	if ((b = argvars[0].vval.v_blob) != NULL
-		&& !tv_check_lock(b->bv_lock,
+		&& !var_check_lock(b->bv_lock,
 					 (char_u *)N_("add() argument"), TRUE))
 	{
 	    int		error = FALSE;
@@ -3579,7 +3579,7 @@
 
 	l1 = argvars[0].vval.v_list;
 	l2 = argvars[1].vval.v_list;
-	if (l1 != NULL && !tv_check_lock(l1->lv_lock, arg_errmsg, TRUE)
+	if (l1 != NULL && !var_check_lock(l1->lv_lock, arg_errmsg, TRUE)
 		&& l2 != NULL)
 	{
 	    if (argvars[2].v_type != VAR_UNKNOWN)
@@ -3615,7 +3615,7 @@
 
 	d1 = argvars[0].vval.v_dict;
 	d2 = argvars[1].vval.v_dict;
-	if (d1 != NULL && !tv_check_lock(d1->dv_lock, arg_errmsg, TRUE)
+	if (d1 != NULL && !var_check_lock(d1->dv_lock, arg_errmsg, TRUE)
 		&& d2 != NULL)
 	{
 	    /* Check the third argument. */
@@ -7266,8 +7266,9 @@
     }
     else if (argvars[0].v_type != VAR_LIST)
 	semsg(_(e_listblobarg), "insert()");
-    else if ((l = argvars[0].vval.v_list) != NULL && !tv_check_lock(l->lv_lock,
-				      (char_u *)N_("insert() argument"), TRUE))
+    else if ((l = argvars[0].vval.v_list) != NULL
+	    && !var_check_lock(l->lv_lock,
+				     (char_u *)N_("insert() argument"), TRUE))
     {
 	if (argvars[2].v_type != VAR_UNKNOWN)
 	    before = (long)tv_get_number_chk(&argvars[2], &error);
@@ -9698,7 +9699,7 @@
 	if (argvars[2].v_type != VAR_UNKNOWN)
 	    semsg(_(e_toomanyarg), "remove()");
 	else if ((d = argvars[0].vval.v_dict) != NULL
-		&& !tv_check_lock(d->dv_lock, arg_errmsg, TRUE))
+		&& !var_check_lock(d->dv_lock, arg_errmsg, TRUE))
 	{
 	    key = tv_get_string_chk(&argvars[1]);
 	    if (key != NULL)
@@ -9781,7 +9782,7 @@
     else if (argvars[0].v_type != VAR_LIST)
 	semsg(_(e_listdictblobarg), "remove()");
     else if ((l = argvars[0].vval.v_list) != NULL
-			       && !tv_check_lock(l->lv_lock, arg_errmsg, TRUE))
+			      && !var_check_lock(l->lv_lock, arg_errmsg, TRUE))
     {
 	idx = (long)tv_get_number_chk(&argvars[1], &error);
 	if (error)
@@ -10128,7 +10129,7 @@
     if (argvars[0].v_type != VAR_LIST)
 	semsg(_(e_listblobarg), "reverse()");
     else if ((l = argvars[0].vval.v_list) != NULL
-	    && !tv_check_lock(l->lv_lock,
+	    && !var_check_lock(l->lv_lock,
 				    (char_u *)N_("reverse() argument"), TRUE))
     {
 	li = l->lv_last;
@@ -12112,7 +12113,7 @@
     else
     {
 	l = argvars[0].vval.v_list;
-	if (l == NULL || tv_check_lock(l->lv_lock,
+	if (l == NULL || var_check_lock(l->lv_lock,
 	     (char_u *)(sort ? N_("sort() argument") : N_("uniq() argument")),
 									TRUE))
 	    goto theend;
diff --git a/src/proto/eval.pro b/src/proto/eval.pro
index 1e673e3..ba75f07 100644
--- a/src/proto/eval.pro
+++ b/src/proto/eval.pro
@@ -103,8 +103,8 @@
 int var_check_ro(int flags, char_u *name, int use_gettext);
 int var_check_fixed(int flags, char_u *name, int use_gettext);
 int var_check_func_name(char_u *name, int new_var);
+int var_check_lock(int lock, char_u *name, int use_gettext);
 int valid_varname(char_u *varname);
-int tv_check_lock(int lock, char_u *name, int use_gettext);
 void copy_tv(typval_T *from, typval_T *to);
 int item_copy(typval_T *from, typval_T *to, int deep, int copyID);
 void get_user_input(typval_T *argvars, typval_T *rettv, int inputdialog, int secret);
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index e263115..67163e6 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -2062,9 +2062,9 @@
   for in_opt in in_opts
     let x = copy(in_opt)
     for out_opt in out_opts
-      call extend(x, out_opt)
+      let x = extend(copy(x), out_opt)
       for err_opt in err_opts
-        call extend(x, err_opt)
+        let x = extend(copy(x), err_opt)
         let opts += [extend({'pty': 1}, x)]
       endfor
     endfor
diff --git a/src/testdir/test_let.vim b/src/testdir/test_let.vim
index 550655c..40eabb8 100644
--- a/src/testdir/test_let.vim
+++ b/src/testdir/test_let.vim
@@ -142,7 +142,7 @@
   call assert_fails('call s:set_varg4(1)', 'E742:')
   call s:set_varg5([0])
   call assert_fails('call s:set_varg6(1)', 'E742:')
-  " call assert_fails('call s:set_varg7(1)', 'E46:')
+  call assert_fails('call s:set_varg7(1)', 'E742:')
   call assert_fails('call s:set_varg8(1)', 'E742:')
   call s:set_varg9([0])
 endfunction
diff --git a/src/userfunc.c b/src/userfunc.c
index d1ea33a..a293dd6 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -2394,11 +2394,11 @@
 	if (fudi.fd_di == NULL)
 	{
 	    /* Can't add a function to a locked dictionary */
-	    if (tv_check_lock(fudi.fd_dict->dv_lock, eap->arg, FALSE))
+	    if (var_check_lock(fudi.fd_dict->dv_lock, eap->arg, FALSE))
 		goto erret;
 	}
 	    /* Can't change an existing function if it is locked */
-	else if (tv_check_lock(fudi.fd_di->di_tv.v_lock, eap->arg, FALSE))
+	else if (var_check_lock(fudi.fd_di->di_tv.v_lock, eap->arg, FALSE))
 	    goto erret;
 
 	/* Give the function a sequential number.  Can only be used with a
diff --git a/src/version.c b/src/version.c
index 6e3c6f4..6e3d780 100644
--- a/src/version.c
+++ b/src/version.c
@@ -784,6 +784,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    897,
+/**/
     896,
 /**/
     895,