diff --git a/amp.php b/amp.php
index c3b48806efd..0b6001e75ca 100644
--- a/amp.php
+++ b/amp.php
@@ -127,10 +127,11 @@ function amp_force_query_var_value( $query_vars ) {
  * @return void
  */
 function amp_maybe_add_actions() {
+	$is_amp_endpoint = is_amp_endpoint();
 
 	// Add hooks for when a themes that support AMP.
 	if ( current_theme_supports( 'amp' ) ) {
-		if ( amp_is_canonical() || is_amp_endpoint() ) {
+		if ( $is_amp_endpoint ) {
 			AMP_Theme_Support::init();
 		} else {
 			amp_add_frontend_actions();
@@ -143,8 +144,6 @@ function amp_maybe_add_actions() {
 		return;
 	}
 
-	$is_amp_endpoint = is_amp_endpoint();
-
 	// Cannot use `get_queried_object` before canonical redirect; see <https://core.trac.wordpress.org/ticket/35344>.
 	global $wp_query;
 	$post = $wp_query->post;
diff --git a/includes/amp-frontend-actions.php b/includes/amp-frontend-actions.php
index 8252bdb5700..f62b93f6b70 100644
--- a/includes/amp-frontend-actions.php
+++ b/includes/amp-frontend-actions.php
@@ -28,6 +28,5 @@ function amp_frontend_add_canonical() {
 		return;
 	}
 
-	$amp_url = amp_get_permalink( get_queried_object_id() );
-	printf( '<link rel="amphtml" href="%s">', esc_url( $amp_url ) );
+	printf( '<link rel="amphtml" href="%s">', esc_url( amp_get_permalink( get_queried_object_id() ) ) );
 }
diff --git a/includes/class-amp-theme-support.php b/includes/class-amp-theme-support.php
index 6592e5aa04f..889e7e91f8d 100644
--- a/includes/class-amp-theme-support.php
+++ b/includes/class-amp-theme-support.php
@@ -12,6 +12,11 @@
  */
 class AMP_Theme_Support {
 
+	/**
+	 * Replaced with the necessary scripts depending on components used in output.
+	 *
+	 * @var string
+	 */
 	const COMPONENT_SCRIPTS_PLACEHOLDER = '<!--AMP_COMPONENT_SCRIPTS_PLACEHOLDER-->';
 
 	/**
@@ -45,10 +50,9 @@ class AMP_Theme_Support {
 	public static function init() {
 		require_once AMP__DIR__ . '/includes/amp-post-template-actions.php';
 		if ( amp_is_canonical() ) {
-			$is_amp_endpoint = ( false !== get_query_var( AMP_QUERY_VAR, false ) ); // Because is_amp_endpoint() now returns true if amp_is_canonical().
 
 			// Permanently redirect to canonical URL if the AMP URL was loaded, since canonical is now AMP.
-			if ( $is_amp_endpoint ) {
+			if ( false !== get_query_var( AMP_QUERY_VAR, false ) ) { // Because is_amp_endpoint() now returns true if amp_is_canonical().
 				wp_safe_redirect( self::get_current_canonical_url(), 301 );
 				exit;
 			}
@@ -76,7 +80,7 @@ public static function is_paired_available() {
 		$args = array_shift( $support );
 
 		if ( isset( $args['available_callback'] ) && is_callable( $args['available_callback'] ) ) {
-			return $args['available_callback']();
+			return call_user_func( $args['available_callback'] );
 		}
 		return true;
 	}