diff --git a/lib/core/utils/dq-element.js b/lib/core/utils/dq-element.js
index 93498e91..373675e3 100644
--- a/lib/core/utils/dq-element.js
+++ b/lib/core/utils/dq-element.js
@@ -246,6 +246,9 @@ DqElement.prototype = {
    * @return {String}
    */
   get selector() {
+    if (axe._cache.get('targetFormat') === 'ancestry') {
+      return this.spec.selector || [getAncestry(this.element)];
+    }
     if (axe._cache.get('runTypeAOpt')) {
       return this.spec.selector || [generateSelectorWithShadow(this.element)];
     }
diff --git a/lib/core/utils/get-ancestry.js b/lib/core/utils/get-ancestry.js
index b80edb93..7321a6da 100644
--- a/lib/core/utils/get-ancestry.js
+++ b/lib/core/utils/get-ancestry.js
@@ -13,8 +13,28 @@ function generateAncestry(node) {
     nodeName !== 'body' &&
     parent.children.length > 1
   ) {
-    const index = Array.prototype.indexOf.call(parent.children, node) + 1;
-    nthChild = `:nth-child(${index})`;
+    let index = 0;
+    if (parent.nodeName === 'BODY') {
+      let count = 0;
+      // Single pass over siblings: count valid children & locate node position.
+      for (
+        let sib = parent.firstElementChild;
+        sib;
+        sib = sib.nextElementSibling
+      ) {
+        if (sib.hasAttribute('data-percy-injected')) {
+          continue;
+        }
+        count++;
+        if (sib === node) {
+          index = count;
+        }
+      }
+      nthChild = count > 1 ? `:nth-child(${index})` : '';
+    } else {
+      index = Array.prototype.indexOf.call(parent.children, node) + 1;
+      nthChild = `:nth-child(${index})`;
+    }
   }
 
   return generateAncestry(parent) + ' > ' + nodeName + nthChild;