diff --git a/src/renderers/dom/fiber/ReactDOMFiberEntry.js b/src/renderers/dom/fiber/ReactDOMFiberEntry.js
index e01fff18f0f8..96c4a92cc4f9 100644
--- a/src/renderers/dom/fiber/ReactDOMFiberEntry.js
+++ b/src/renderers/dom/fiber/ReactDOMFiberEntry.js
@@ -74,10 +74,10 @@ findDOMNode._injectFiber(function(fiber: Fiber) {
 
 type DOMContainer =
   | (Element & {
-    _reactRootContainer: ?Object,
+    _reactRootContainer: ?Object
   })
   | (Document & {
-    _reactRootContainer: ?Object,
+    _reactRootContainer: ?Object
   });
 
 type Container = Element | Document;
@@ -539,12 +539,7 @@ function renderSubtreeIntoContainer(
       const hostInstance = DOMRenderer.findHostInstance(
         container._reactRootContainer.current,
       );
-      const hostInstanceParentNode: any =
-        hostInstance && hostInstance.parentNode;
-      const hostInstanceParentIsPortal =
-        hostInstanceParentNode &&
-        hostInstanceParentNode.__reactInternalIsPortalContainer;
-      if (hostInstance && !hostInstanceParentIsPortal) {
+      if (hostInstance) {
         warning(
           hostInstance.parentNode === container,
           'render(...): It looks like the React-rendered content of this ' +
diff --git a/src/renderers/dom/fiber/__tests__/__snapshots__/ReactDOMFiber-test.js.snap b/src/renderers/dom/fiber/__tests__/__snapshots__/ReactDOMFiber-test.js.snap
new file mode 100644
index 000000000000..55f93688b35c
--- /dev/null
+++ b/src/renderers/dom/fiber/__tests__/__snapshots__/ReactDOMFiber-test.js.snap
@@ -0,0 +1,3 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`ReactDOMFiber should warn when replacing a container which was manually updated outside of React 1`] = `""`;
diff --git a/src/renderers/shared/fiber/ReactFiberTreeReflection.js b/src/renderers/shared/fiber/ReactFiberTreeReflection.js
index 3e557375bb21..ce6e0a354bac 100644
--- a/src/renderers/shared/fiber/ReactFiberTreeReflection.js
+++ b/src/renderers/shared/fiber/ReactFiberTreeReflection.js
@@ -25,10 +25,11 @@ if (__DEV__) {
 }
 
 var {
-  HostRoot,
+  ClassComponent,
   HostComponent,
+  HostRoot,
+  HostPortal,
   HostText,
-  ClassComponent,
 } = require('ReactTypeOfWork');
 
 var {NoEffect, Placement} = require('ReactTypeOfSideEffect');
@@ -241,8 +242,7 @@ exports.findCurrentHostFiber = function(parent: Fiber): Fiber | null {
   while (true) {
     if (node.tag === HostComponent || node.tag === HostText) {
       return node;
-    } else if (node.child) {
-      // TODO: If we hit a Portal, we're supposed to skip it.
+    } else if (node.child && node.tag !== HostPortal) {
       node.child.return = node;
       node = node.child;
       continue;