diff --git a/webf/lib/src/rendering/widget.dart b/webf/lib/src/rendering/widget.dart
index d6d94129f4..1ef09e65c2 100644
--- a/webf/lib/src/rendering/widget.dart
+++ b/webf/lib/src/rendering/widget.dart
@@ -89,8 +89,32 @@ class RenderWidget extends RenderBoxModel
     final double verticalBorder =
         renderStyle.effectiveBorderTopWidth.computedValue +
             renderStyle.effectiveBorderBottomWidth.computedValue;
+    // Prefer the most restrictive finite constraints available:
+    // - our own incoming constraints (when bounded)
+    // - the outer Flutter widget constraints (when embedded via WebFWidgetElementChild)
+    // - the root viewport size as a final fallback
+    double effectiveViewportWidth = viewportSize.width;
+    double effectiveViewportHeight = viewportSize.height;
+
+    final RenderWidgetElementChild? widgetElementChild = findWidgetElementChild();
+    final BoxConstraints? widgetConstraints = widgetElementChild?.effectiveChildConstraints;
+    if (widgetConstraints != null) {
+      if (widgetConstraints.hasBoundedWidth && widgetConstraints.maxWidth.isFinite) {
+        effectiveViewportWidth = math.min(effectiveViewportWidth, widgetConstraints.maxWidth);
+      }
+      if (widgetConstraints.hasBoundedHeight && widgetConstraints.maxHeight.isFinite) {
+        effectiveViewportHeight = math.min(effectiveViewportHeight, widgetConstraints.maxHeight);
+      }
+    }
+
+    if (constraints.hasBoundedWidth) {
+      effectiveViewportWidth = math.min(effectiveViewportWidth, constraints.maxWidth);
+    }
+    if (constraints.hasBoundedHeight) {
+      effectiveViewportHeight = math.min(effectiveViewportHeight, constraints.maxHeight);
+    }
     final double contentViewportHeight =
-        math.max(0.0, viewportSize.height - verticalPadding - verticalBorder);
+        math.max(0.0, effectiveViewportHeight - verticalPadding - verticalBorder);
 
     BoxConstraints childConstraints;
     if (isInlineBlockAutoWidth || hasExplicitInlineWidth) {
@@ -108,7 +132,7 @@ class RenderWidget extends RenderBoxModel
           maxWidth: (contentConstraints!.hasTightWidth ||
                   (renderStyle.target as WidgetElement).allowsInfiniteWidth)
               ? contentConstraints!.maxWidth
-              : math.min(viewportSize.width, contentConstraints!.maxWidth),
+              : math.min(effectiveViewportWidth, contentConstraints!.maxWidth),
           minHeight: contentConstraints!.minHeight,
           maxHeight: (contentConstraints!.hasTightHeight ||
                   (renderStyle.target as WidgetElement).allowsInfiniteHeight)
diff --git a/webf/test/src/rendering/render_widget_constraints_test.dart b/webf/test/src/rendering/render_widget_constraints_test.dart
new file mode 100644
index 0000000000..8c12913b2c
--- /dev/null
+++ b/webf/test/src/rendering/render_widget_constraints_test.dart
@@ -0,0 +1,225 @@
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:webf/dom.dart' as dom;
+import 'package:webf/rendering.dart';
+import 'package:webf/webf.dart';
+import 'package:webf/widget.dart';
+import '../widget/test_utils.dart';
+import '../../setup.dart';
+
+class _TestConstraintsWidgetElement extends WidgetElement {
+  _TestConstraintsWidgetElement(super.context);
+
+  static BoxConstraints? lastLayoutConstraints;
+
+  @override
+  WebFWidgetElementState createState() {
+    return _TestConstraintsWidgetElementState(this);
+  }
+}
+
+class _TestConstraintsWidgetElementState extends WebFWidgetElementState {
+  _TestConstraintsWidgetElementState(super.widgetElement);
+
+  @override
+  Widget build(BuildContext context) {
+    return LayoutBuilder(builder: (BuildContext context, BoxConstraints constraints) {
+      _TestConstraintsWidgetElement.lastLayoutConstraints = constraints;
+      // Avoid SizedBox.expand so this test widget remains safe even if a bug
+      // accidentally forwards unbounded constraints.
+      return const SizedBox.shrink();
+    });
+  }
+}
+
+class _TestConstraintsHostWidgetElement extends WidgetElement {
+  _TestConstraintsHostWidgetElement(super.context);
+
+  @override
+  WebFWidgetElementState createState() {
+    return _TestConstraintsHostWidgetElementState(this);
+  }
+}
+
+class _TestConstraintsHostWidgetElementState extends WebFWidgetElementState {
+  _TestConstraintsHostWidgetElementState(super.widgetElement);
+
+  @override
+  _TestConstraintsHostWidgetElement get widgetElement => super.widgetElement as _TestConstraintsHostWidgetElement;
+
+  @override
+  Widget build(BuildContext context) {
+    return SizedBox(
+      height: 200,
+      child: WebFWidgetElementChild(
+        child: WebFHTMLElement(
+          tagName: 'DIV',
+          controller: widgetElement.controller,
+          parentElement: widgetElement,
+          children: widgetElement.childNodes.toWidgetList(),
+        ),
+      ),
+    );
+  }
+}
+
+class _ProbeEmbedder extends StatefulWidget {
+  const _ProbeEmbedder({
+    required this.controllerName,
+    required this.webf,
+  });
+
+  final String controllerName;
+  final Widget webf;
+
+  @override
+  State<_ProbeEmbedder> createState() => _ProbeEmbedderState();
+}
+
+class _ProbeEmbedderState extends State<_ProbeEmbedder> {
+  WidgetElement? _probe;
+
+  @override
+  void initState() {
+    super.initState();
+    _scheduleProbeMount();
+  }
+
+  void _scheduleProbeMount() {
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (!mounted || _probe != null) return;
+
+      final WebFController? controller =
+          WebFControllerManager.instance.getControllerSync(widget.controllerName);
+      final dom.Element? element = controller?.view.document.getElementById(const ['probe']);
+      if (element is! WidgetElement) {
+        _scheduleProbeMount();
+        return;
+      }
+
+      element.parentNode?.removeChild(element);
+      setState(() {
+        _TestConstraintsWidgetElement.lastLayoutConstraints = null;
+        _probe = element;
+      });
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Stack(
+      children: <Widget>[
+        Positioned.fill(child: widget.webf),
+        if (_probe != null)
+          Positioned(
+            left: 0,
+            right: 0,
+            top: 0,
+            height: 200,
+            child: Align(
+              alignment: Alignment.topLeft,
+              child: WebFWidgetElementChild(
+                child: _probe!.toWidget(),
+              ),
+            ),
+          ),
+      ],
+    );
+  }
+}
+
+void main() {
+  const String kProbeTagName = 'WEBF-TEST-CONSTRAINTS-WIDGET';
+  const String kHostTagName = 'WEBF-TEST-CONSTRAINTS-HOST';
+
+  setUpAll(() {
+    setupTest();
+    if (!dom.getAllWidgetElements().containsKey(kProbeTagName)) {
+      dom.defineWidgetElement(
+        kProbeTagName,
+        (context) => _TestConstraintsWidgetElement(context),
+      );
+    }
+    if (!dom.getAllWidgetElements().containsKey(kHostTagName)) {
+      dom.defineWidgetElement(
+        kHostTagName,
+        (context) => _TestConstraintsHostWidgetElement(context),
+      );
+    }
+  });
+
+  testWidgets('RenderWidget clamps child constraints to parent max', (WidgetTester tester) async {
+    final String controllerName = 'render-widget-constraints-${DateTime.now().millisecondsSinceEpoch}';
+    _TestConstraintsWidgetElement.lastLayoutConstraints = null;
+
+    await WebFWidgetTestUtils.prepareWidgetTest(
+      tester: tester,
+      controllerName: controllerName,
+      viewportWidth: 360,
+      viewportHeight: 640,
+        html: '''
+        <body>
+          <webf-test-constraints-widget id="probe"></webf-test-constraints-widget>
+        </body>
+      ''',
+      wrap: (Widget webf) => Directionality(
+        textDirection: TextDirection.ltr,
+        child: _ProbeEmbedder(controllerName: controllerName, webf: webf),
+      ),
+    );
+
+    // Give the embedder time to detach the probe from DOM and remount it under a bounded parent.
+    for (int i = 0; i < 10 && _TestConstraintsWidgetElement.lastLayoutConstraints == null; i++) {
+      await tester.pump(const Duration(milliseconds: 50));
+    }
+
+    final BoxConstraints? constraints = _TestConstraintsWidgetElement.lastLayoutConstraints;
+    expect(constraints, isNotNull);
+    expect(constraints!.maxHeight, closeTo(200.0, 0.01));
+  });
+
+  testWidgets('RenderWidget uses WebFWidgetElementChild constraints when unbounded', (WidgetTester tester) async {
+    final String controllerName = 'render-widget-wrapper-constraints-${DateTime.now().millisecondsSinceEpoch}';
+    _TestConstraintsWidgetElement.lastLayoutConstraints = null;
+
+    final prepared = await WebFWidgetTestUtils.prepareWidgetTest(
+      tester: tester,
+      controllerName: controllerName,
+      viewportWidth: 360,
+      viewportHeight: 640,
+      html: '''
+        <body>
+          <webf-test-constraints-host id="host">
+            <div id="wrapper">
+              <webf-test-constraints-widget id="probe"></webf-test-constraints-widget>
+            </div>
+          </webf-test-constraints-host>
+        </body>
+      ''',
+      wrap: (Widget webf) => Directionality(
+        textDirection: TextDirection.ltr,
+        child: webf,
+      ),
+    );
+
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 100));
+
+    // Ensure the widget element is being laid out with an unbounded height by WebF layout.
+    final dom.Element probe = prepared.getElementById('probe');
+    final RenderObject? probeRenderer = probe.attachedRenderer;
+    expect(probeRenderer, isNotNull);
+    RenderObject? current = probeRenderer;
+    while (current != null && current is! RenderBoxModel) {
+      current = current.parent as RenderObject?;
+    }
+    expect(current, isA<RenderBoxModel>());
+    expect((current! as RenderBoxModel).constraints.maxHeight.isInfinite, isTrue);
+
+    // Despite the unbounded WebF constraints, the hosted Flutter widget must be clamped
+    // by the outer WebFWidgetElementChild (SizedBox(height: 200)).
+    final BoxConstraints? constraints = _TestConstraintsWidgetElement.lastLayoutConstraints;
+    expect(constraints, isNotNull);
+    expect(constraints!.maxHeight, closeTo(200.0, 0.01));
+  });
+}