diff --git a/src/renderers/dom/fiber/ReactDOMFiberComponent.js b/src/renderers/dom/fiber/ReactDOMFiberComponent.js
index b31104d479c28..dda1bfa846c8d 100644
--- a/src/renderers/dom/fiber/ReactDOMFiberComponent.js
+++ b/src/renderers/dom/fiber/ReactDOMFiberComponent.js
@@ -59,9 +59,10 @@ var STYLE = 'style';
 var HTML = '__html';
 
 var {
-  html: HTML_NAMESPACE,
-  svg: SVG_NAMESPACE,
-  mathml: MATH_NAMESPACE,
+  Namespaces: {
+    html: HTML_NAMESPACE,
+  },
+  getIntrinsicNamespace,
 } = DOMNamespaces;
 
 if (__DEV__) {
@@ -295,32 +296,7 @@ function updateDOMProperties(
   }
 }
 
-// Assumes there is no parent namespace.
-function getIntrinsicNamespace(type: string): string {
-  switch (type) {
-    case 'svg':
-      return SVG_NAMESPACE;
-    case 'math':
-      return MATH_NAMESPACE;
-    default:
-      return HTML_NAMESPACE;
-  }
-}
-
 var ReactDOMFiberComponent = {
-  getChildNamespace(parentNamespace: string | null, type: string): string {
-    if (parentNamespace == null || parentNamespace === HTML_NAMESPACE) {
-      // No (or default) parent namespace: potential entry point.
-      return getIntrinsicNamespace(type);
-    }
-    if (parentNamespace === SVG_NAMESPACE && type === 'foreignObject') {
-      // We're leaving SVG.
-      return HTML_NAMESPACE;
-    }
-    // By default, pass namespace below.
-    return parentNamespace;
-  },
-
   createElement(
     type: *,
     props: Object,
@@ -343,6 +319,8 @@ var ReactDOMFiberComponent = {
     }
     if (namespaceURI === HTML_NAMESPACE) {
       if (__DEV__) {
+        // Should this check be gated by parent namespace? Not sure we want to
+        // allow <SVG> or <mATH>.
         warning(
           isCustomComponentTag || type === type.toLowerCase(),
           '<%s /> is using uppercase HTML. Always use lowercase HTML tags ' +
diff --git a/src/renderers/dom/fiber/ReactDOMFiberEntry.js b/src/renderers/dom/fiber/ReactDOMFiberEntry.js
index b9af1b9ea4e99..6225a76587851 100644
--- a/src/renderers/dom/fiber/ReactDOMFiberEntry.js
+++ b/src/renderers/dom/fiber/ReactDOMFiberEntry.js
@@ -15,6 +15,7 @@
 import type {Fiber} from 'ReactFiber';
 import type {ReactNodeList} from 'ReactTypes';
 
+var DOMNamespaces = require('DOMNamespaces');
 var ExecutionEnvironment = require('fbjs/lib/ExecutionEnvironment');
 var ReactBrowserEventEmitter = require('ReactBrowserEventEmitter');
 var ReactControlledComponent = require('ReactControlledComponent');
@@ -44,8 +45,10 @@ var findDOMNode = require('findDOMNode');
 var invariant = require('fbjs/lib/invariant');
 
 var {
-  createElement,
   getChildNamespace,
+} = DOMNamespaces;
+var {
+  createElement,
   setInitialProperties,
   diffProperties,
   updateProperties,
diff --git a/src/renderers/dom/shared/DOMNamespaces.js b/src/renderers/dom/shared/DOMNamespaces.js
index e93d53e919618..07b852152858a 100644
--- a/src/renderers/dom/shared/DOMNamespaces.js
+++ b/src/renderers/dom/shared/DOMNamespaces.js
@@ -11,10 +11,41 @@
 
 'use strict';
 
-var DOMNamespaces = {
-  html: 'http://www.w3.org/1999/xhtml',
-  mathml: 'http://www.w3.org/1998/Math/MathML',
-  svg: 'http://www.w3.org/2000/svg',
+const HTML_NAMESPACE = 'http://www.w3.org/1999/xhtml';
+const MATH_NAMESPACE = 'http://www.w3.org/1998/Math/MathML';
+const SVG_NAMESPACE = 'http://www.w3.org/2000/svg';
+
+const Namespaces = {
+  html: HTML_NAMESPACE,
+  mathml: MATH_NAMESPACE,
+  svg: SVG_NAMESPACE,
 };
 
-module.exports = DOMNamespaces;
+// Assumes there is no parent namespace.
+function getIntrinsicNamespace(type: string): string {
+  switch (type) {
+    case 'svg':
+      return SVG_NAMESPACE;
+    case 'math':
+      return MATH_NAMESPACE;
+    default:
+      return HTML_NAMESPACE;
+  }
+}
+
+function getChildNamespace(parentNamespace: string | null, type: string): string {
+  if (parentNamespace == null || parentNamespace === HTML_NAMESPACE) {
+    // No (or default) parent namespace: potential entry point.
+    return getIntrinsicNamespace(type);
+  }
+  if (parentNamespace === SVG_NAMESPACE && type === 'foreignObject') {
+    // We're leaving SVG.
+    return HTML_NAMESPACE;
+  }
+  // By default, pass namespace below.
+  return parentNamespace;
+}
+
+exports.Namespaces = Namespaces;
+exports.getIntrinsicNamespace = getIntrinsicNamespace;
+exports.getChildNamespace = getChildNamespace;
diff --git a/src/renderers/dom/shared/__tests__/ReactServerRendering-test.js b/src/renderers/dom/shared/__tests__/ReactServerRendering-test.js
index 60ea2e7b2c80d..e2e90dda1c9c4 100644
--- a/src/renderers/dom/shared/__tests__/ReactServerRendering-test.js
+++ b/src/renderers/dom/shared/__tests__/ReactServerRendering-test.js
@@ -772,4 +772,36 @@ describe('ReactDOMServer', () => {
       );
     }).toThrowError(/Cannot assign to read only property.*/);
   });
+
+  it('warns about lowercase html but not in svg tags', () => {
+    spyOn(console, 'error');
+    function CompositeG(props) {
+      // Make sure namespace passes through composites
+      return <g>{props.children}</g>;
+    }
+    ReactDOMServer.renderToStaticMarkup(
+      <div>
+        <inPUT />
+        <svg>
+          <CompositeG>
+            <linearGradient />
+            <foreignObject>
+              {/* back to HTML */}
+              <iFrame />
+            </foreignObject>
+          </CompositeG>
+        </svg>
+      </div>,
+    );
+    expect(console.error.calls.count()).toBe(2);
+    expect(console.error.calls.argsFor(0)[0]).toBe(
+      'Warning: <inPUT /> is using uppercase HTML. Always use lowercase ' +
+      'HTML tags in React.'
+    );
+    // linearGradient doesn't warn
+    expect(console.error.calls.argsFor(1)[0]).toBe(
+      'Warning: <iFrame /> is using uppercase HTML. Always use lowercase ' +
+      'HTML tags in React.'
+    );
+  });
 });
diff --git a/src/renderers/dom/shared/setInnerHTML.js b/src/renderers/dom/shared/setInnerHTML.js
index d5cbb20109792..f2645392d8f1f 100644
--- a/src/renderers/dom/shared/setInnerHTML.js
+++ b/src/renderers/dom/shared/setInnerHTML.js
@@ -11,7 +11,7 @@
 
 'use strict';
 
-var DOMNamespaces = require('DOMNamespaces');
+var Namespaces = require('DOMNamespaces').Namespaces;
 var createMicrosoftUnsafeLocalFunction = require('createMicrosoftUnsafeLocalFunction');
 
 // SVG temp container for IE lacking innerHTML
@@ -28,7 +28,7 @@ var setInnerHTML = createMicrosoftUnsafeLocalFunction(function(node, html) {
   // IE does not have innerHTML for SVG nodes, so instead we inject the
   // new markup in a temp node and then move the child nodes across into
   // the target node
-  if (node.namespaceURI === DOMNamespaces.svg && !('innerHTML' in node)) {
+  if (node.namespaceURI === Namespaces.svg && !('innerHTML' in node)) {
     reusableSVGContainer =
       reusableSVGContainer || document.createElement('div');
     reusableSVGContainer.innerHTML = '<svg>' + html + '</svg>';
diff --git a/src/renderers/dom/shared/utils/__tests__/setInnerHTML-test.js b/src/renderers/dom/shared/utils/__tests__/setInnerHTML-test.js
index 1f703f97e5a34..0cdcb1b1460e7 100644
--- a/src/renderers/dom/shared/utils/__tests__/setInnerHTML-test.js
+++ b/src/renderers/dom/shared/utils/__tests__/setInnerHTML-test.js
@@ -13,7 +13,7 @@
 
 // TODO: can we express this test with only public API?
 var setInnerHTML = require('setInnerHTML');
-var DOMNamespaces = require('DOMNamespaces');
+var Namespaces = require('DOMNamespaces').Namespaces;
 
 describe('setInnerHTML', () => {
   describe('when the node has innerHTML property', () => {
@@ -31,7 +31,7 @@ describe('setInnerHTML', () => {
     xit('sets innerHTML on it', () => {
       // Create a mock node that looks like an SVG in IE (without innerHTML)
       var node = {
-        namespaceURI: DOMNamespaces.svg,
+        namespaceURI: Namespaces.svg,
         appendChild: jasmine.createSpy(),
       };
 
diff --git a/src/renderers/dom/stack/client/DOMLazyTree.js b/src/renderers/dom/stack/client/DOMLazyTree.js
index 6e2fb0c94b1c9..8a398a4cd59c4 100644
--- a/src/renderers/dom/stack/client/DOMLazyTree.js
+++ b/src/renderers/dom/stack/client/DOMLazyTree.js
@@ -11,7 +11,7 @@
 
 'use strict';
 
-var DOMNamespaces = require('DOMNamespaces');
+var Namespaces = require('DOMNamespaces').Namespaces;
 var setInnerHTML = require('setInnerHTML');
 var {DOCUMENT_FRAGMENT_NODE, ELEMENT_NODE} = require('HTMLNodeType');
 var createMicrosoftUnsafeLocalFunction = require('createMicrosoftUnsafeLocalFunction');
@@ -68,7 +68,7 @@ var insertTreeBefore = createMicrosoftUnsafeLocalFunction(function(
     (tree.node.nodeType === ELEMENT_NODE &&
       tree.node.nodeName.toLowerCase() === 'object' &&
       (tree.node.namespaceURI == null ||
-        tree.node.namespaceURI === DOMNamespaces.html))
+        tree.node.namespaceURI === Namespaces.html))
   ) {
     insertTreeChildren(tree);
     parentNode.insertBefore(tree.node, referenceNode);
diff --git a/src/renderers/dom/stack/client/ReactDOMComponent.js b/src/renderers/dom/stack/client/ReactDOMComponent.js
index f5f63a67c6dd2..e4bfecc946c10 100644
--- a/src/renderers/dom/stack/client/ReactDOMComponent.js
+++ b/src/renderers/dom/stack/client/ReactDOMComponent.js
@@ -14,7 +14,7 @@
 var AutoFocusUtils = require('AutoFocusUtils');
 var CSSPropertyOperations = require('CSSPropertyOperations');
 var DOMLazyTree = require('DOMLazyTree');
-var DOMNamespaces = require('DOMNamespaces');
+var Namespaces = require('DOMNamespaces').Namespaces;
 var DOMMarkupOperations = require('DOMMarkupOperations');
 var DOMProperty = require('DOMProperty');
 var DOMPropertyOperations = require('DOMPropertyOperations');
@@ -512,11 +512,11 @@ ReactDOMComponent.Mixin = {
     }
     if (
       namespaceURI == null ||
-      (namespaceURI === DOMNamespaces.svg && parentTag === 'foreignobject')
+      (namespaceURI === Namespaces.svg && parentTag === 'foreignobject')
     ) {
-      namespaceURI = DOMNamespaces.html;
+      namespaceURI = Namespaces.html;
     }
-    if (namespaceURI === DOMNamespaces.html) {
+    if (namespaceURI === Namespaces.html) {
       if (__DEV__) {
         warning(
           isCustomComponentTag || this._tag === this._currentElement.type,
@@ -526,9 +526,9 @@ ReactDOMComponent.Mixin = {
         );
       }
       if (this._tag === 'svg') {
-        namespaceURI = DOMNamespaces.svg;
+        namespaceURI = Namespaces.svg;
       } else if (this._tag === 'math') {
-        namespaceURI = DOMNamespaces.mathml;
+        namespaceURI = Namespaces.mathml;
       }
     }
     this._namespaceURI = namespaceURI;
@@ -557,7 +557,7 @@ ReactDOMComponent.Mixin = {
     if (transaction.useCreateElement) {
       var ownerDocument = hostContainerInfo._ownerDocument;
       var el;
-      if (namespaceURI === DOMNamespaces.html) {
+      if (namespaceURI === Namespaces.html) {
         if (this._tag === 'script') {
           // Create the script via .innerHTML so its "parser-inserted" flag is
           // set to true and it does not execute
@@ -587,7 +587,7 @@ ReactDOMComponent.Mixin = {
           );
           didWarnShadyDOM = true;
         }
-        if (this._namespaceURI === DOMNamespaces.html) {
+        if (this._namespaceURI === Namespaces.html) {
           if (
             !isCustomComponentTag &&
             Object.prototype.toString.call(el) ===
diff --git a/src/renderers/shared/server/ReactPartialRenderer.js b/src/renderers/shared/server/ReactPartialRenderer.js
index c2ac0f75cd786..64cdb8109b9a5 100644
--- a/src/renderers/shared/server/ReactPartialRenderer.js
+++ b/src/renderers/shared/server/ReactPartialRenderer.js
@@ -11,6 +11,11 @@
 
 'use strict';
 
+var {
+  Namespaces,
+  getIntrinsicNamespace,
+  getChildNamespace,
+} = require('DOMNamespaces');
 var DOMMarkupOperations = require('DOMMarkupOperations');
 var React = require('react');
 var ReactControlledValuePropTypes = require('ReactControlledValuePropTypes');
@@ -443,6 +448,9 @@ class ReactDOMServerRenderer {
   constructor(element, makeStaticMarkup) {
     var children = React.isValidElement(element) ? [element] : toArray(element);
     var topFrame = {
+      // Assume all trees start in the HTML namespace (not totally true, but
+      // this is what we did historically)
+      domNamespace: Namespaces.html,
       children,
       childIndex: 0,
       context: emptyObject,
@@ -483,7 +491,7 @@ class ReactDOMServerRenderer {
       if (__DEV__) {
         setCurrentDebugStack(this.stack);
       }
-      out += this.render(child, frame.context);
+      out += this.render(child, frame.context, frame.domNamespace);
       if (__DEV__) {
         // TODO: Handle reentrant server render calls. This doesn't.
         resetCurrentDebugStack();
@@ -492,7 +500,7 @@ class ReactDOMServerRenderer {
     return out;
   }
 
-  render(child, context) {
+  render(child, context, parentNamespace) {
     if (typeof child === 'string' || typeof child === 'number') {
       var text = '' + child;
       if (text === '') {
@@ -512,10 +520,11 @@ class ReactDOMServerRenderer {
         return '';
       } else {
         if (React.isValidElement(child)) {
-          return this.renderDOM(child, context);
+          return this.renderDOM(child, context, parentNamespace);
         } else {
           var children = toArray(child);
           var frame = {
+            domNamespace: parentNamespace,
             children,
             childIndex: 0,
             context: context,
@@ -531,16 +540,25 @@ class ReactDOMServerRenderer {
     }
   }
 
-  renderDOM(element, context) {
+  renderDOM(element, context, parentNamespace) {
     var tag = element.type.toLowerCase();
 
+    let namespace = parentNamespace;
+    if (parentNamespace === Namespaces.html) {
+      namespace = getIntrinsicNamespace(tag);
+    }
+
     if (__DEV__) {
-      warning(
-        tag === element.type,
-        '<%s /> is using uppercase HTML. Always use lowercase HTML tags ' +
-          'in React.',
-        element.type,
-      );
+      if (namespace === Namespaces.html) {
+        // Should this check be gated by parent namespace? Not sure we want to
+        // allow <SVG> or <mATH>.
+        warning(
+          tag === element.type,
+          '<%s /> is using uppercase HTML. Always use lowercase HTML tags ' +
+            'in React.',
+          element.type,
+        );
+      }
     }
 
     validateDangerousTag(tag);
@@ -801,6 +819,7 @@ class ReactDOMServerRenderer {
       children = toArray(props.children);
     }
     var frame = {
+      domNamespace: getChildNamespace(parentNamespace, element.type),
       tag,
       children,
       childIndex: 0,