diff --git a/dom/svg/SVGMPathElement.cpp b/dom/svg/SVGMPathElement.cpp
index 9a86dc4f158d..1431c8324a1e 100644
--- a/dom/svg/SVGMPathElement.cpp
+++ b/dom/svg/SVGMPathElement.cpp
@@ -77,7 +77,7 @@ nsresult SVGMPathElement::BindToTree(Document* aDocument, nsIContent* aParent,
       SVGMPathElementBase::BindToTree(aDocument, aParent, aBindingParent);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  if (aDocument) {
+  if (IsInComposedDoc()) {
     const nsAttrValue* hrefAttrValue =
         HasAttr(kNameSpaceID_None, nsGkAtoms::href)
             ? mAttrs.GetAttr(nsGkAtoms::href, kNameSpaceID_None)
@@ -103,7 +103,7 @@ bool SVGMPathElement::ParseAttribute(int32_t aNamespaceID, nsAtom* aAttribute,
       aNamespaceID, aAttribute, aValue, aMaybeScriptedPrincipal, aResult);
   if ((aNamespaceID == kNameSpaceID_XLink ||
        aNamespaceID == kNameSpaceID_None) &&
-      aAttribute == nsGkAtoms::href && IsInUncomposedDoc()) {
+      aAttribute == nsGkAtoms::href && IsInComposedDoc()) {
     // Note: If we fail the IsInDoc call, it's ok -- we'll update the target
     // on next BindToTree call.
 
diff --git a/layout/reftests/svg/smil/motion/animateMotion-mpath-shadow.svg b/layout/reftests/svg/smil/motion/animateMotion-mpath-shadow.svg
new file mode 100644
index 000000000000..d57aa1a29f66
--- /dev/null
+++ b/layout/reftests/svg/smil/motion/animateMotion-mpath-shadow.svg
@@ -0,0 +1,34 @@
+<svg xmlns="http://www.w3.org/2000/svg"
+     xmlns:xlink="http://www.w3.org/1999/xlink" class="reftest-wait">
+  <title>Test that pathLength works inside a shadow tree</title>
+  <defs>
+    <path id="path" pathLength="100" d="M0,0 h400" />
+    <g id="content">
+      <rect width="100%" height="100%" fill="lime"/>
+
+      <!-- calcMode="linear" -->
+      <rect x="10" y="10" width="100" height="100" fill="red"/>
+      <rect x="-190" y="10" width="100" height="100" fill="lime">
+        <animateMotion begin="100s" dur="1s" keyPoints="0;1" keyTimes="0;1" calcMode="linear">
+          <mpath xlink:href="#path" />
+        </animateMotion>
+      </rect>
+
+      <!-- calcMode="paced" -->
+      <rect x="10" y="110" width="100" height="100" fill="red"/>
+      <rect x="-190" y="110" width="100" height="100" fill="lime">
+        <animateMotion begin="100s" dur="1s">
+          <mpath xlink:href="#path" />
+        </animateMotion>
+      </rect>
+    </g>
+  </defs>
+  <script xlink:href="../smil-util.js" type="text/javascript"/>
+  <script type="text/javascript">
+    function doTest() {
+      setTimeAndSnapshot(100.5, true);
+    }
+    window.addEventListener("MozReftestInvalidate", doTest, false);
+  </script>
+  <use xlink:href="#content"></use>
+</svg>
diff --git a/layout/reftests/svg/smil/motion/reftest.list b/layout/reftests/svg/smil/motion/reftest.list
index b9668c09495b..5acfeab8bc8f 100644
--- a/layout/reftests/svg/smil/motion/reftest.list
+++ b/layout/reftests/svg/smil/motion/reftest.list
@@ -19,3 +19,4 @@ fuzzy-if(skiaContent,0-1,0-30) == animateMotion-values-paced-1b.svg animateMotio
 == animateMotion-mpath-pathLength-1.svg lime.svg
 == animateMotion-mpath-targetChange-1.svg lime.svg
 == animateMotion-mpath-target-transform-1.svg lime.svg
+== animateMotion-mpath-shadow.svg lime.svg