diff --git a/packages/htmljs/html.js b/packages/htmljs/html.js
index 9f4594b2f7..a0078fb8b0 100644
--- a/packages/htmljs/html.js
+++ b/packages/htmljs/html.js
@@ -186,11 +186,14 @@ HTML.EmitCode = function (value) {
   this.value = value;
 };
 
+HTML.isTagEnsured = function (t) {
+  return HTML.isKnownElement(t) || HTML.isKnownSVGElement(t);
+};
+
 (function () {
   for (var i = 0; i < HTML.knownElementNames.length; i++)
     HTML.ensureTag(HTML.knownElementNames[i]);
 
   for (var i = 0; i < HTML.knownSVGElementNames.length; i++)
     HTML.ensureTag(HTML.knownSVGElementNames[i]);
-
 })();
diff --git a/packages/spacebars/spacebars.js b/packages/spacebars/spacebars.js
index b41a1dba97..10d15a801a 100644
--- a/packages/spacebars/spacebars.js
+++ b/packages/spacebars/spacebars.js
@@ -507,9 +507,10 @@ var optimize = function (tree) {
       return null;
     } else if (node instanceof HTML.Tag) {
 
-      if (node.tagName === 'TEXTAREA') {
+      if (node.tagName === 'TEXTAREA' || (! HTML.isKnownElement(node.tagName))) {
         // optimizing into a TEXTAREA's RCDATA would require being a little
-        // more clever.
+        // more clever.  foreign elements like SVG can't be stringified for
+        // innerHTML.
         return node;
       }
 
@@ -935,19 +936,20 @@ Spacebars.compile = function (input, options) {
 };
 
 Spacebars.codeGen = function (parseTree, options) {
-  var tree = parseTree;
-
-  if (isTemplate)
-    // optimizing fragments would require being smarter about whether we are
-    // in a TEXTAREA, say.
-    tree = optimize(tree);
-
-  tree = replaceSpecials(tree);
-
   // is this a template, rather than a block passed to
   // a block helper, say
   var isTemplate = (options && options.isTemplate);
 
+  var tree = parseTree;
+
+  if (isTemplate) {
+    // optimizing fragments would require being smarter about whether we are
+    // in a TEXTAREA, say.
+    tree = optimize(tree);
+  }
+
+  tree = replaceSpecials(tree);
+
   var code = '(function () { var self = this; ';
   if (isTemplate) {
     // support `{{> content}}` and `{{> elseContent}}` with
diff --git a/packages/spacebars/tojs.js b/packages/spacebars/tojs.js
index 34288ef101..d8629a5de0 100644
--- a/packages/spacebars/tojs.js
+++ b/packages/spacebars/tojs.js
@@ -44,7 +44,7 @@ HTML.Tag.prototype.toJS = function (options) {
   }
 
   var tagSymbol = this.tagName;
-  if ((this instanceof HTML.Tag) && ! HTML.isKnownElement(tagSymbol))
+  if ((this instanceof HTML.Tag) && ! HTML.isTagEnsured(tagSymbol))
     tagSymbol = 'HTML.getTag(' + toJSLiteral(tagSymbol) + ')';
   else
     tagSymbol = 'HTML.' + tagSymbol;