diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 4ebf65a..151ffed 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -192,6 +192,13 @@
   v9.CheckDefFailure(lines, 'E1307: Argument 1: Trying to modify a const list<number>')
 
   lines =<< trim END
+      final l = [1, 2]
+      add(l, 3)
+      assert_equal([1, 2, 3], l)
+  END
+  v9.CheckDefSuccess(lines)
+
+  lines =<< trim END
       const b = 0z0102
       add(b,  0z03)
   END
@@ -1209,6 +1216,13 @@
   END
   v9.CheckDefFailure(lines, 'E1307: Argument 1: Trying to modify a const dict<number>')
 
+  lines =<< trim END
+      final d = {a: 1, b: 2}
+      extend(d, {c: 3})
+      assert_equal({a: 1, b: 2, c: 3}, d)
+  END
+  v9.CheckDefSuccess(lines)
+
   # item in a for loop is const
   lines =<< trim END
       var l: list<dict<any>> = [{n: 1}]
diff --git a/src/version.c b/src/version.c
index 40dad23..a2e66b2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    627,
+/**/
     626,
 /**/
     625,
diff --git a/src/vim.h b/src/vim.h
index 8f1bf33..14f67f7 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -2250,6 +2250,7 @@
 } estack_arg_T;
 
 // Flags for assignment functions.
+#define ASSIGN_VAR	0     // ":var" (nothing special)
 #define ASSIGN_FINAL	0x01  // ":final"
 #define ASSIGN_CONST	0x02  // ":const"
 #define ASSIGN_NO_DECL	0x04  // "name = expr" without ":let"/":const"/":final"
diff --git a/src/vim9.h b/src/vim9.h
index 176fc64..fe193b1 100644
--- a/src/vim9.h
+++ b/src/vim9.h
@@ -697,7 +697,9 @@
     int		lv_loop_depth;	// depth for variable inside a loop or -1
     int		lv_loop_idx;	// index of first variable inside a loop or -1
     int		lv_from_outer;	// nesting level, using ctx_outer scope
-    int		lv_const;	// when TRUE cannot be assigned to
+    int		lv_const;	// ASSIGN_VAR (can be assigned to),
+				// ASSIGN_FINAL (no assignment) or ASSIGN_CONST
+				// (value cannot be changed)
     int		lv_arg;		// when TRUE this is an argument
 } lvar_T;
 
diff --git a/src/vim9cmds.c b/src/vim9cmds.c
index c9c222c..3c561d1 100644
--- a/src/vim9cmds.c
+++ b/src/vim9cmds.c
@@ -881,7 +881,7 @@
 
     // Reserve a variable to store the loop iteration counter and initialize it
     // to -1.
-    loop_lvar = reserve_local(cctx, (char_u *)"", 0, FALSE, &t_number);
+    loop_lvar = reserve_local(cctx, (char_u *)"", 0, ASSIGN_VAR, &t_number);
     if (loop_lvar == NULL)
     {
 	drop_scope(cctx);
@@ -894,7 +894,7 @@
     // Reserve a variable to store ec_funcrefs.ga_len, used in ISN_ENDLOOP.
     // The variable index is always the loop var index plus one.
     // It is not used when no closures are encountered, we don't know yet.
-    funcref_lvar = reserve_local(cctx, (char_u *)"", 0, FALSE, &t_number);
+    funcref_lvar = reserve_local(cctx, (char_u *)"", 0, ASSIGN_VAR, &t_number);
     if (funcref_lvar == NULL)
     {
 	drop_scope(cctx);
@@ -1050,7 +1050,8 @@
 			&& need_type_where(item_type, lhs_type, -1,
 					    where, cctx, FALSE, FALSE) == FAIL)
 		    goto failed;
-		var_lvar = reserve_local(cctx, arg, varlen, TRUE, lhs_type);
+		var_lvar = reserve_local(cctx, arg, varlen, ASSIGN_CONST,
+								     lhs_type);
 		if (var_lvar == NULL)
 		    // out of memory or used as an argument
 		    goto failed;
@@ -1182,7 +1183,7 @@
 
     // Reserve a variable to store ec_funcrefs.ga_len, used in ISN_ENDLOOP.
     // It is not used when no closures are encountered, we don't know yet.
-    funcref_lvar = reserve_local(cctx, (char_u *)"", 0, FALSE, &t_number);
+    funcref_lvar = reserve_local(cctx, (char_u *)"", 0, ASSIGN_VAR, &t_number);
     if (funcref_lvar == NULL)
     {
 	drop_scope(cctx);
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 5225345..53c8e5a 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -471,7 +471,7 @@
 {
     type_T	*type = type_arg;
 
-    if (lvar->lv_const && (type->tt_flags & TTFLAG_CONST) == 0)
+    if (lvar->lv_const == ASSIGN_CONST && (type->tt_flags & TTFLAG_CONST) == 0)
     {
 	if (type->tt_flags & TTFLAG_STATIC)
 	    // entry in static_types[] is followed by const type
@@ -487,6 +487,8 @@
 
 /*
  * Reserve space for a local variable.
+ * "assign" can be ASSIGN_VAR for :var, ASSIGN_CONST for :const and
+ * ASSIGN_FINAL for :final.
  * Return the variable or NULL if it failed.
  */
     lvar_T *
@@ -494,7 +496,7 @@
 	cctx_T	*cctx,
 	char_u	*name,
 	size_t	len,
-	int	isConst,
+	int	assign,
 	type_T	*type)
 {
     lvar_T  *lvar;
@@ -519,7 +521,7 @@
     lvar->lv_idx = dfunc->df_var_names.ga_len;
 
     lvar->lv_name = vim_strnsave(name, len == 0 ? STRLEN(name) : len);
-    lvar->lv_const = isConst;
+    lvar->lv_const = assign;
     if (type == &t_unknown || type == &t_any)
 	// type not known yet, may be inferred from RHS
 	lvar->lv_type = type;
@@ -993,7 +995,7 @@
     {
 	// Define a local variable for the function reference.
 	lvar = reserve_local(cctx, func_name, name_end - name_start,
-						    TRUE, ufunc->uf_func_type);
+					    ASSIGN_CONST, ufunc->uf_func_type);
 	if (lvar == NULL)
 	    goto theend;
 	if (generate_FUNCREF(cctx, ufunc, &funcref_isn) == FAIL)
@@ -1691,8 +1693,10 @@
 	    return FAIL;
 
 	// New local variable.
+	int assign = cmdidx == CMD_final ? ASSIGN_FINAL
+			     : cmdidx == CMD_const ? ASSIGN_CONST : ASSIGN_VAR;
 	lhs->lhs_lvar = reserve_local(cctx, var_start, lhs->lhs_varlen,
-		    cmdidx == CMD_final || cmdidx == CMD_const, lhs->lhs_type);
+							assign, lhs->lhs_type);
 	if (lhs->lhs_lvar == NULL)
 	    return FAIL;
 	lhs->lhs_new_local = TRUE;
@@ -1769,7 +1773,8 @@
 	return FAIL;
     }
     if (!is_decl && lhs->lhs_lvar != NULL
-			   && lhs->lhs_lvar->lv_const && !lhs->lhs_has_index)
+			   && lhs->lhs_lvar->lv_const != ASSIGN_VAR
+			   && !lhs->lhs_has_index)
     {
 	semsg(_(e_cannot_assign_to_constant), lhs->lhs_name);
 	return FAIL;