diff --git a/internal/compiler/expression_tree.rs b/internal/compiler/expression_tree.rs
index 7c6c03cfc..e33fac2e6 100644
--- a/internal/compiler/expression_tree.rs
+++ b/internal/compiler/expression_tree.rs
@@ -1130,7 +1130,26 @@ impl Expression {
                 nr.mark_as_set();
                 let lookup = nr.element().borrow().lookup_property(nr.name());
                 if lookup.is_valid_for_assignment() {
-                    true
+                    if !nr
+                        .element()
+                        .borrow()
+                        .property_analysis
+                        .borrow()
+                        .get(nr.name())
+                        .map_or(false, |d| d.is_linked_to_read_only)
+                    {
+                        true
+                    } else if is_legacy_component {
+                        diag.push_warning("Modifying a property that is linked to a read-only property is deprecated".into(), node);
+                        true
+                    } else {
+                        diag.push_error(
+                            "Cannot modify a property that is linked to a read-only property"
+                                .into(),
+                            node,
+                        );
+                        false
+                    }
                 } else if is_legacy_component
                     && lookup.property_visibility == PropertyVisibility::Output
                 {
diff --git a/internal/compiler/langtype.rs b/internal/compiler/langtype.rs
index 5f362af3f..fa3168c07 100644
--- a/internal/compiler/langtype.rs
+++ b/internal/compiler/langtype.rs
@@ -346,7 +346,7 @@ pub struct BuiltinPropertyInfo {
 
 impl BuiltinPropertyInfo {
     pub fn new(ty: Type) -> Self {
-        Self { ty, default_value: None, property_visibility: PropertyVisibility::Private }
+        Self { ty, default_value: None, property_visibility: PropertyVisibility::InOut }
     }
 
     pub fn is_native_output(&self) -> bool {
diff --git a/internal/compiler/load_builtins.rs b/internal/compiler/load_builtins.rs
index 5eb68cfc2..9318e099a 100644
--- a/internal/compiler/load_builtins.rs
+++ b/internal/compiler/load_builtins.rs
@@ -86,6 +86,8 @@ pub fn load_builtins(register: &mut TypeRegister) {
                         register,
                     ));
 
+                    info.property_visibility = PropertyVisibility::Private;
+
                     for token in p.children_with_tokens() {
                         if token.kind() != SyntaxKind::Identifier {
                             continue;
diff --git a/internal/compiler/object_tree.rs b/internal/compiler/object_tree.rs
index 1a354fe0b..6a56d8886 100644
--- a/internal/compiler/object_tree.rs
+++ b/internal/compiler/object_tree.rs
@@ -614,6 +614,9 @@ pub struct PropertyAnalysis {
 
     /// true if this property is read from another component
     pub is_read_externally: bool,
+
+    /// True if the property is linked to another property that is read only. That property becomes read-only
+    pub is_linked_to_read_only: bool,
 }
 
 impl PropertyAnalysis {
@@ -1233,7 +1236,7 @@ impl Element {
                     && lookup_result.property_visibility == PropertyVisibility::Output
                 {
                     diag.push_warning(
-                        format!("Assigning to out property '{unresolved_name}' is deprecated"),
+                        format!("Assigning to output property '{unresolved_name}' is deprecated"),
                         &name_token,
                     );
                 } else {
diff --git a/internal/compiler/passes/resolving.rs b/internal/compiler/passes/resolving.rs
index d67b8bda4..99f097dc3 100644
--- a/internal/compiler/passes/resolving.rs
+++ b/internal/compiler/passes/resolving.rs
@@ -30,7 +30,6 @@ fn resolve_expression(
     scope: &ComponentScope,
     type_register: &TypeRegister,
     type_loader: &crate::typeloader::TypeLoader,
-    two_ways: &mut Vec<(String, NamedReference)>,
     diag: &mut BuildDiagnostics,
 ) {
     if let Expression::Uncompiled(node) = expr {
@@ -59,14 +58,7 @@ fn resolve_expression(
                 Expression::from_binding_expression_node(node.clone(), &mut lookup_ctx)
             }
             SyntaxKind::TwoWayBinding => {
-                if lookup_ctx.property_type == Type::Invalid {
-                    // An attempt to resolve this already failed when trying to resolve the property type
-                    assert!(diag.has_error());
-                    return;
-                }
-                if let Some(nr) = resolve_two_way_binding(node.clone().into(), &mut lookup_ctx) {
-                    two_ways.push((property_name.unwrap().into(), nr));
-                }
+                assert!(diag.has_error(), "Two way binding should have been resolved already  (property: {property_name:?})");
                 Expression::Invalid
             }
             _ => {
@@ -83,6 +75,8 @@ pub fn resolve_expressions(
     type_loader: &crate::typeloader::TypeLoader,
     diag: &mut BuildDiagnostics,
 ) {
+    resolve_two_way_bindings(doc, &doc.local_registry, diag);
+
     for component in doc.inner_components.iter() {
         let scope = ComponentScope(vec![]);
 
@@ -90,7 +84,6 @@ pub fn resolve_expressions(
             let mut new_scope = scope.clone();
             let mut is_repeated = elem.borrow().repeated.is_some();
             new_scope.0.push(elem.clone());
-            let mut two_ways = vec![];
             visit_element_expressions(elem, |expr, property_name, property_type| {
                 if is_repeated {
                     // The first expression is always the model and it needs to be resolved with the parent scope
@@ -102,7 +95,6 @@ pub fn resolve_expressions(
                         &scope,
                         &doc.local_registry,
                         type_loader,
-                        &mut two_ways,
                         diag,
                     );
                     is_repeated = false;
@@ -114,14 +106,10 @@ pub fn resolve_expressions(
                         &new_scope,
                         &doc.local_registry,
                         type_loader,
-                        &mut two_ways,
                         diag,
                     )
                 }
             });
-            for (prop, nr) in two_ways {
-                elem.borrow().bindings.get(&prop).unwrap().borrow_mut().two_way_bindings.push(nr);
-            }
             new_scope
         })
     }
@@ -1139,6 +1127,123 @@ fn maybe_lookup_object(
     base
 }
 
+/// Go through all the two way binding and resolve them first
+fn resolve_two_way_bindings(
+    doc: &Document,
+    type_register: &TypeRegister,
+    diag: &mut BuildDiagnostics,
+) {
+    for component in doc.inner_components.iter() {
+        let scope = ComponentScope(vec![]);
+
+        recurse_elem(&component.root_element, &scope, &mut |elem, scope| {
+            let mut new_scope = scope.clone();
+            new_scope.0.push(elem.clone());
+            for (prop_name, binding) in &elem.borrow().bindings {
+                let mut binding = binding.borrow_mut();
+                if let Expression::Uncompiled(node) = binding.expression.clone() {
+                    if let Some(n) = syntax_nodes::TwoWayBinding::new(node.clone()) {
+                        let lhs_lookup = elem.borrow().lookup_property(prop_name);
+                        if lhs_lookup.property_type == Type::Invalid {
+                            // An attempt to resolve this already failed when trying to resolve the property type
+                            assert!(diag.has_error());
+                            continue;
+                        }
+                        let mut lookup_ctx = LookupCtx {
+                            property_name: Some(prop_name.as_str()),
+                            property_type: lhs_lookup.property_type.clone(),
+                            component_scope: &new_scope.0,
+                            diag,
+                            arguments: vec![],
+                            type_register,
+                            type_loader: None,
+                            current_token: Some(node.clone().into()),
+                        };
+
+                        binding.expression = Expression::Invalid;
+
+                        if let Some(nr) = resolve_two_way_binding(n, &mut lookup_ctx) {
+                            binding.two_way_bindings.push(nr.clone());
+
+                            // Check the compatibility.
+                            let rhs_lookup = nr.element().borrow().lookup_property(nr.name());
+
+                            if !rhs_lookup.is_valid_for_assignment() {
+                                match (
+                                    lhs_lookup.property_visibility,
+                                    rhs_lookup.property_visibility,
+                                ) {
+                                    (PropertyVisibility::Input, PropertyVisibility::Input)
+                                        if !lhs_lookup.is_local_to_component =>
+                                    {
+                                        assert!(rhs_lookup.is_local_to_component);
+                                        marked_linked_read_only(elem, prop_name);
+                                    }
+                                    (
+                                        PropertyVisibility::Output | PropertyVisibility::Private,
+                                        PropertyVisibility::Output | PropertyVisibility::Input,
+                                    ) => {
+                                        assert!(lhs_lookup.is_local_to_component);
+                                        marked_linked_read_only(elem, prop_name);
+                                    }
+                                    (PropertyVisibility::Input, PropertyVisibility::Output)
+                                        if !lhs_lookup.is_local_to_component =>
+                                    {
+                                        assert!(!rhs_lookup.is_local_to_component);
+                                        marked_linked_read_only(elem, prop_name);
+                                    }
+                                    _ => {
+                                        if lookup_ctx.is_legacy_component() {
+                                            diag.push_warning(
+                                                format!(
+                                                    "Link to a {} property is deprecated",
+                                                    rhs_lookup.property_visibility
+                                                ),
+                                                &node,
+                                            );
+                                        } else {
+                                            diag.push_error(
+                                                format!(
+                                                    "Cannot link to a {} property",
+                                                    rhs_lookup.property_visibility
+                                                ),
+                                                &node,
+                                            )
+                                        }
+                                    }
+                                }
+                            } else if !lhs_lookup.is_valid_for_assignment() {
+                                if rhs_lookup.is_local_to_component
+                                    && rhs_lookup.property_visibility == PropertyVisibility::InOut
+                                {
+                                    if lookup_ctx.is_legacy_component() {
+                                        debug_assert!(!diag.is_empty()); // warning should already be reported
+                                    } else {
+                                        diag.push_error("Cannot link input property".into(), &node);
+                                    }
+                                } else {
+                                    // This is allowed, but then the rhs must also become read only.
+                                    marked_linked_read_only(&nr.element(), nr.name());
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+            new_scope
+        })
+    }
+
+    fn marked_linked_read_only(elem: &ElementRc, prop_name: &str) {
+        elem.borrow()
+            .property_analysis
+            .borrow_mut()
+            .entry(prop_name.to_string())
+            .or_default()
+            .is_linked_to_read_only = true;
+    }
+}
+
 pub fn resolve_two_way_binding(
     node: syntax_nodes::TwoWayBinding,
     ctx: &mut LookupCtx,
diff --git a/internal/compiler/tests/syntax/new_syntax/input_output2.slint b/internal/compiler/tests/syntax/new_syntax/input_output2.slint
index 376348da5..ee9e7ca3e 100644
--- a/internal/compiler/tests/syntax/new_syntax/input_output2.slint
+++ b/internal/compiler/tests/syntax/new_syntax/input_output2.slint
@@ -45,7 +45,7 @@ OldCompo := Rectangle {
 //          ^warning{Self assignment on an output property is deprecated}
         }
         has-hover: true;
-//      ^warning{Assigning to out property 'has-hover' is deprecated}
+//      ^warning{Assigning to output property 'has-hover' is deprecated}
     }
 }
 
diff --git a/internal/compiler/tests/syntax/new_syntax/two_way_input_output.slint b/internal/compiler/tests/syntax/new_syntax/two_way_input_output.slint
new file mode 100644
index 000000000..f9bbd42eb
--- /dev/null
+++ b/internal/compiler/tests/syntax/new_syntax/two_way_input_output.slint
@@ -0,0 +1,325 @@
+// Copyright © SixtyFPS GmbH <info@slint-ui.com>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+component Button {
+    in property<bool> enabled : true;
+    out property <bool> pressed;
+    in-out property <bool> checked;
+    callback clicked();
+}
+
+component C1 {
+    out property <bool> out;
+    in property <bool> in;
+    in-out property <bool> inout;
+    property <bool> priv;
+
+    // pressed is "output" in Button
+    out <=> b.pressed;  // ok  (but then there should be no other assignment?)
+    in <=> b.pressed; // Error
+//  ^error{Cannot link to a output property}
+    inout <=> b.pressed;
+//  ^error{Cannot link to a output property}
+    priv <=> b.pressed; // makes assignment forbidden
+
+
+
+    b:= Button {
+        clicked => {
+            in = !in;
+//          ^error{Assignment on a input property}
+            out = !out;
+//          ^error{Cannot modify a property that is linked to a read-only property}
+            inout = !inout;
+            priv = !priv;
+//          ^error{Cannot modify a property that is linked to a read-only property}
+
+            self.enabled = !self.enabled;
+            self.checked = !self.checked;
+            self.pressed = !self.pressed;
+//          ^error{Assignment on a output property}
+
+        }
+    }
+
+}
+
+
+  component C2 {
+    out property <bool> out;
+    in property <bool> in;
+    in-out property <bool> inout;
+    property <bool> priv;
+
+    // enabled is "input" in Button
+    out <=> b.enabled;
+    in <=> b.enabled;
+    inout <=> b.enabled;
+    priv <=> b.enabled;
+
+    b:= Button {
+        clicked => {
+            in = !in;
+//          ^error{Assignment on a input property}
+            out = !out;
+            inout = !inout;
+            priv = !priv;
+
+
+            self.enabled = !self.enabled;
+//          ^error{Cannot modify a property that is linked to a read-only property}
+            self.checked = !self.checked;
+            self.pressed = !self.pressed;
+//          ^error{Assignment on a output property}
+
+        }
+    }
+}
+
+component C3 {
+    out property <bool> out;
+    in property <bool> in;
+    in-out property <bool> inout;
+    property <bool> priv;
+
+    // checked is "input/output" in Button
+    out <=> b.checked;
+    in <=> b.checked;
+    inout <=> b.checked;
+    priv <=> b.checked;
+
+    b:= Button {
+        clicked => {
+            in = !in;
+//          ^error{Assignment on a input property}
+            out = !out;
+            inout = !inout;
+            priv = !priv;
+
+            self.enabled = !self.enabled;
+            self.checked = !self.checked;
+//          ^error{Cannot modify a property that is linked to a read-only property}
+            self.pressed = !self.pressed;
+//          ^error{Assignment on a output property}
+        }
+    }
+}
+
+
+component C5 {
+    out property <bool> out;
+    in property <bool> in;
+    in-out property <bool> inout;
+    property <bool> priv;
+
+    Button { enabled <=> out; }
+    Button {
+        enabled <=> in;
+        clicked => { self.enabled = !self.enabled; }
+//                   ^error{Cannot modify a property that is linked to a read-only property}
+    }
+    Button { enabled <=> inout; }
+    Button { enabled <=> priv; }
+}
+
+component C6 {
+    out property <bool> out;
+    in property <bool> in;
+    in-out property <bool> inout;
+    property <bool> priv;
+
+    Button {
+        checked <=> out;
+        clicked => { out = !out; self.checked = !self.checked; }
+    }
+    Button {
+        checked <=> in;
+//      ^error{Cannot link to a input property}
+        clicked => { self.checked = !self.checked; }
+    }
+    Button {
+        checked <=> inout;
+        clicked => { inout = !inout; self.checked = !self.checked; }
+    }
+    Button {
+        checked <=> priv;
+        clicked => { priv = !priv; self.checked = !self.checked; }
+    }
+}
+
+component C7 {
+    b1 := Button {
+        clicked => {
+            self.enabled = !self.enabled;
+            self.checked = !self.checked;
+            self.pressed = !self.pressed;
+//          ^error{Assignment on a output property}
+        }
+    }
+    Button {
+        enabled <=> b1.pressed;
+        clicked => { self.enabled = !self.enabled; }
+//                   ^error{Cannot modify a property that is linked to a read-only property}
+    }
+    b2 := Button {
+        clicked => {
+            self.enabled = !self.enabled;
+            self.checked = !self.checked;
+            self.pressed = !self.pressed;
+//          ^error{Assignment on a output property}
+        }
+    }
+    Button { checked <=> b2.pressed;  }
+//           ^error{Cannot link to a output property}
+
+    b3 := Button {
+        clicked => {
+            self.enabled = !self.enabled;
+            self.checked = !self.checked;
+            self.pressed = !self.pressed;
+//          ^error{Assignment on a output property}
+        }
+    }
+    Button {
+        checked <=> b3.checked;
+        enabled <=> b3.checked;
+    }
+    Button {
+        checked <=> b3.enabled;
+        enabled <=> b3.enabled;
+    }
+}
+
+component C8 {
+    out property <bool> out1;
+    out property <bool> out2;
+    out property <bool> out3;
+    out property <bool> out4;
+
+    out property <bool> out <=> out1;
+    in property <bool> in <=> out2;
+    in-out property <bool> inout <=> out3;
+    property <bool> priv <=> out4;
+
+    Button {
+        clicked => {
+            out1 = !out1;
+            out2 = !out2;
+//          ^error{Cannot modify a property that is linked to a read-only property}
+            out3 = !out3;
+            out4 = !out4;
+        }
+    }
+}
+
+component C9 {
+    in property <bool> in1;
+    in property <bool> in2;
+    in property <bool> in3;
+    in property <bool> in4;
+
+    out property <bool> out <=> in1;
+    in property <bool> in <=> in2;
+//                        ^error{Cannot link to a input property}
+    in-out property <bool> inout <=> in3;
+//                               ^error{Cannot link to a input property}
+    property <bool> priv <=> in4;
+
+    Button {
+        clicked => {
+            out = !out;
+//          ^error{Cannot modify a property that is linked to a read-only property}
+            in = !in;
+//          ^error{Assignment on a input property}
+            inout = !inout;
+            priv = !priv;
+//          ^error{Cannot modify a property that is linked to a read-only property}
+        }
+    }
+}
+
+
+component C10 {
+    in-out property <bool> inout1;
+    in-out property <bool> inout2;
+    in-out property <bool> inout3;
+    in-out property <bool> inout4;
+
+    out property <bool> out <=> inout1;
+    in property <bool> in <=> inout2;
+//                        ^error{Cannot link input property}
+    in-out property <bool> inout <=> inout3;
+    property <bool> priv <=> inout4;
+
+    Button {
+        clicked => {
+            inout1 = !inout1;
+            inout2 = !inout2;
+            inout3 = !inout3;
+            inout4 = !inout4;
+            out = !out;
+            in = !in;
+//          ^error{Assignment on a input property}
+            inout = !inout;
+            priv = !priv;
+        }
+    }
+}
+
+component C11 {
+    property <bool> priv1;
+    property <bool> priv2;
+    property <bool> priv3;
+    property <bool> priv4;
+
+    out property <bool> out <=> priv1;
+    in property <bool> in <=> priv2;
+    in-out property <bool> inout <=> priv3;
+    property <bool> priv <=> priv4;
+
+    Button {
+        clicked => {
+            priv1 = !priv1;
+            priv2 = !priv2;
+//          ^error{Cannot modify a property that is linked to a read-only property}
+            priv3 = !priv3;
+            priv4 = !priv4;
+            out = !out;
+            in = !in;
+//          ^error{Assignment on a input property}
+            inout = !inout;
+            priv = !priv;
+        }
+    }
+}
+
+Legacy1 := Rectangle {
+    b1:= Button {}
+    in property in1 <=> b1.pressed;
+//                  ^warning{Link to a output property is deprecated}
+    out property out1 <=> b1.pressed;
+    in-out property inout1 <=> b1.pressed;
+//                         ^warning{Link to a output property is deprecated}
+
+
+    property <bool> p1;
+    Button {
+        pressed <=> p1;
+//      ^warning{Assigning to output property 'pressed' is deprecated}
+        clicked => {
+            p1 = !p1;
+            out1 = !out1;
+//          ^warning{Modifying a property that is linked to a read-only property is deprecated}
+        }
+    }
+    Button {
+        enabled <=> self.pressed;
+        clicked => {
+            self.enabled = !self.enabled;
+//          ^warning{Modifying a property that is linked to a read-only property is deprecated}
+        }
+    }
+
+
+}
+
diff --git a/internal/compiler/widgets/common/common.slint b/internal/compiler/widgets/common/common.slint
index f6d889f7a..54a62d959 100644
--- a/internal/compiler/widgets/common/common.slint
+++ b/internal/compiler/widgets/common/common.slint
@@ -11,7 +11,7 @@ export LineEditInner := Rectangle {
     property text <=> input.text;
     property placeholder-color <=> placeholder.color;
     property enabled <=> input.enabled;
-    property has-focus <=> input.has-focus;
+    property <bool> has-focus: input.has-focus;
     property input-type <=> input.input-type;
     property horizontal-alignment <=> input.horizontal-alignment;
     property read-only <=> input.read-only;
@@ -47,7 +47,7 @@ export LineEditInner := Rectangle {
 export TextEdit := ScrollView {
     property <length> font-size <=> input.font-size;
     property <string> text <=> input.text;
-    has-focus <=> input.has-focus;
+    has-focus: input.has-focus;
     enabled <=> input.enabled;
     property <TextWrap> wrap <=> input.wrap;
     property horizontal-alignment <=> input.horizontal-alignment;
diff --git a/internal/compiler/widgets/fluent-base/std-widgets-impl.slint b/internal/compiler/widgets/fluent-base/std-widgets-impl.slint
index e46c45144..9bbdaf03c 100644
--- a/internal/compiler/widgets/fluent-base/std-widgets-impl.slint
+++ b/internal/compiler/widgets/fluent-base/std-widgets-impl.slint
@@ -83,7 +83,7 @@ export global StyleMetrics := {
 export Button := Rectangle {
     callback clicked;
     property<string> text <=> text.text;
-    property<bool> has-focus <=> fs.has-focus;
+    property<bool> has-focus: fs.has-focus;
     property<bool> pressed: self.enabled && touch.pressed;
     property<bool> enabled <=> touch.enabled;
     property<bool> checkable;
diff --git a/internal/compiler/widgets/fluent-base/std-widgets.slint b/internal/compiler/widgets/fluent-base/std-widgets.slint
index 73e81def1..08c80a524 100644
--- a/internal/compiler/widgets/fluent-base/std-widgets.slint
+++ b/internal/compiler/widgets/fluent-base/std-widgets.slint
@@ -218,7 +218,7 @@ export Slider := Rectangle {
     property<float> maximum: 100;
     property<float> minimum: 0;
     property<float> value;
-    property<bool> has-focus <=> fs.has-focus;
+    property<bool> has-focus: fs.has-focus;
     property<bool> enabled <=> touch.enabled;
     callback changed(float);