diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index fa0c2856a1..0c8cd50e85 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -651,7 +651,12 @@ function wp_scripts_get_suffix( $type = '' ) {
 		// Include an unmodified $wp_version.
 		require ABSPATH . WPINC . '/version.php';
 
-		$develop_src = str_contains( $wp_version, '-src' );
+		/*
+		 * Note: str_contains() is not used here, as this file can be included
+		 * via wp-admin/load-scripts.php or wp-admin/load-styles.php, in which case
+		 * the polyfills from wp-includes/compat.php are not loaded.
+		 */
+		$develop_src = false !== strpos( $wp_version, '-src' );
 
 		if ( ! defined( 'SCRIPT_DEBUG' ) ) {
 			define( 'SCRIPT_DEBUG', $develop_src );
@@ -1480,7 +1485,12 @@ function wp_default_styles( $styles ) {
 	require ABSPATH . WPINC . '/version.php';
 
 	if ( ! defined( 'SCRIPT_DEBUG' ) ) {
-		define( 'SCRIPT_DEBUG', str_contains( $wp_version, '-src' ) );
+		/*
+		 * Note: str_contains() is not used here, as this file can be included
+		 * via wp-admin/load-scripts.php or wp-admin/load-styles.php, in which case
+		 * the polyfills from wp-includes/compat.php are not loaded.
+		 */
+		define( 'SCRIPT_DEBUG', false !== strpos( $wp_version, '-src' ) );
 	}
 
 	$guessurl = site_url();