diff --git a/src/eval.c b/src/eval.c
index 931d51045..93b840e61 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1564,6 +1564,9 @@ get_lval(
 					om->ocm_name);
 				return NULL;
 			    case VIM_ACCESS_READ:
+				// If [idx] or .key following, read only OK.
+				if (*p == '[' || *p == '.')
+				    break;
 				if ((flags & GLV_READ_ONLY) == 0)
 				{
 				    semsg(_(e_member_is_not_writable_str),
diff --git a/src/testdir/test_vim9_class.vim b/src/testdir/test_vim9_class.vim
index 763b5a539..f57bf44d0 100644
--- a/src/testdir/test_vim9_class.vim
+++ b/src/testdir/test_vim9_class.vim
@@ -613,8 +613,63 @@ def Test_assignment_nested_type()
     enddef
 
     Test_assign_to_nested_typed_member()
+
+    var script_inner = Inner.new(0)
+    var script_outer = Outer.new(script_inner)
+    script_outer.inner.value = 1
+    assert_equal(1, script_inner.value)
   END
   v9.CheckSourceSuccess(lines)
+
+  # Assignment where target item is read only in :def
+  lines =<< trim END
+    vim9script
+
+    class Inner
+      this.value: number = 0
+    endclass
+
+    class Outer
+      this.inner: Inner
+    endclass
+
+    def F(outer: Outer)
+      outer.inner.value = 1
+    enddef
+
+    def Test_assign_to_nested_typed_member()
+      var inner = Inner.new(0)
+      var outer = Outer.new(inner)
+      F(outer)
+      assert_equal(1, inner.value)
+    enddef
+
+    Test_assign_to_nested_typed_member()
+  END
+  v9.CheckSourceFailure(lines, 'E46: Cannot change read-only variable "value"')
+
+  # Assignment where target item is read only script level
+  lines =<< trim END
+    vim9script
+
+    class Inner
+      this.value: number = 0
+    endclass
+
+    class Outer
+      this.inner: Inner
+    endclass
+
+    def F(outer: Outer)
+      outer.inner.value = 1
+    enddef
+
+    var script_inner = Inner.new(0)
+    var script_outer = Outer.new(script_inner)
+    script_outer.inner.value = 1
+    assert_equal(1, script_inner.value)
+  END
+  v9.CheckSourceFailure(lines, 'E1335: Member is not writable: value')
 enddef
 
 def Test_assignment_with_operator()
diff --git a/src/version.c b/src/version.c
index ec6cce308..5abc4f733 100644
--- a/src/version.c
+++ b/src/version.c
@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1920,
 /**/
     1919,
 /**/