diff --git a/includes/sanitizers/class-amp-tag-and-attribute-sanitizer.php b/includes/sanitizers/class-amp-tag-and-attribute-sanitizer.php
index 7b21d225ea1..f33df0990e2 100644
--- a/includes/sanitizers/class-amp-tag-and-attribute-sanitizer.php
+++ b/includes/sanitizers/class-amp-tag-and-attribute-sanitizer.php
@@ -2472,7 +2472,7 @@ private function remove_disallowed_siblings( DOMElement $node, $spec_name ) {
 
 		$prev_sibling = $node->previousSibling;
 		while ( null !== $prev_sibling ) {
-			if ( ! ( $prev_sibling instanceof Element ) ) {
+			if ( $prev_sibling instanceof Element ) {
 				$this->remove_invalid_child(
 					$prev_sibling,
 					[
@@ -2487,7 +2487,7 @@ private function remove_disallowed_siblings( DOMElement $node, $spec_name ) {
 
 		$next_sibling = $node->nextSibling;
 		while ( null !== $next_sibling ) {
-			if ( ! ( $next_sibling instanceof Element ) ) {
+			if ( $next_sibling instanceof Element ) {
 				$this->remove_invalid_child(
 					$next_sibling,
 					[