diff --git a/includes/sanitizers/class-amp-tag-and-attribute-sanitizer.php b/includes/sanitizers/class-amp-tag-and-attribute-sanitizer.php
index cc85fe8f50c..ae5971a5aec 100644
--- a/includes/sanitizers/class-amp-tag-and-attribute-sanitizer.php
+++ b/includes/sanitizers/class-amp-tag-and-attribute-sanitizer.php
@@ -255,7 +255,7 @@ public function sanitize() {
 		while ( ! empty( $this->stack ) ) {
 
 			// Get the next node to process.
-			$node = array_pop( $this->stack );
+			$node = array_shift( $this->stack );
 
 			/**
 			 * Process this node.
diff --git a/tests/test-class-amp-theme-support.php b/tests/test-class-amp-theme-support.php
index 645e9654af3..5494b341c2a 100644
--- a/tests/test-class-amp-theme-support.php
+++ b/tests/test-class-amp-theme-support.php
@@ -1524,8 +1524,8 @@ public function test_prepare_response() {
 			'<script type="text/javascript" src="https://cdn.ampproject.org/v0/amp-mathml-latest.js" async custom-element="amp-mathml"></script>',
 
 			// Note these are single-quoted because they are injected after the DOM has been re-serialized, so the type and src attributes come from WP_Scripts::do_item().
-			'<script src="https://cdn.ampproject.org/v0/amp-ad-latest.js" async="" custom-element="amp-ad"></script>',
 			'<script src="https://cdn.ampproject.org/v0/amp-audio-latest.js" async="" custom-element="amp-audio"></script>',
+			'<script src="https://cdn.ampproject.org/v0/amp-ad-latest.js" async="" custom-element="amp-ad"></script>',
 
 			'<link rel="icon" href="http://example.org/favicon.png" sizes="32x32">',
 			'<link rel="icon" href="http://example.org/favicon.png" sizes="192x192">',
diff --git a/tests/test-tag-and-attribute-sanitizer.php b/tests/test-tag-and-attribute-sanitizer.php
index d637cbf2c67..3883434caf4 100644
--- a/tests/test-tag-and-attribute-sanitizer.php
+++ b/tests/test-tag-and-attribute-sanitizer.php
@@ -1060,16 +1060,16 @@ public function test_replace_node_with_children_validation_errors() {
 </div>
 EOB;
 		$expected_errors[] = array(
-			'node_name'       => 'bazfoo',
+			'node_name'       => 'invalid_p',
 			'parent_name'     => 'div',
 			'code'            => 'invalid_element',
-			'node_attributes' => array(),
+			'node_attributes' => array( 'id' => 'invalid' ),
 		);
 		$expected_errors[] = array(
-			'node_name'       => 'invalid_p',
+			'node_name'       => 'bazfoo',
 			'parent_name'     => 'div',
 			'code'            => 'invalid_element',
-			'node_attributes' => array( 'id' => 'invalid' ),
+			'node_attributes' => array(),
 		);
 		$content[]         = <<<EOB
 <ul>