diff --git a/src/wp-admin/customize.php b/src/wp-admin/customize.php
index fdbc7f7b9e..699ecdf914 100644
--- a/src/wp-admin/customize.php
+++ b/src/wp-admin/customize.php
@@ -189,7 +189,7 @@ do_action( 'customize_controls_head' );
 			// Check if the theme requires the FSE to work correctly.
 			$theme_tags = $wp_customize->theme()->get( 'Tags' );
 
-			if ( ! empty( $theme_tags ) && in_array( 'full-site-editing', $theme_tags, true ) && ! is_plugin_active( 'gutenberg/gutenberg.php' ) ) {
+			if ( ! empty( $theme_tags ) && in_array( 'full-site-editing', $theme_tags, true ) && ! function_exists( 'gutenberg_is_fse_theme' ) ) {
 				$fse_safe = false;
 			}
 			?>
diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index cbf1849d21..a1a4af1946 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -911,7 +911,7 @@ function validate_theme_requirements( $stylesheet ) {
 	// If the theme is a Full Site Editing theme, check for the presence of the Gutenberg plugin.
 	$theme_tags = $theme->get( 'Tags' );
 
-	if ( ! empty( $theme_tags ) && in_array( 'full-site-editing', $theme_tags, true ) && ! is_plugin_active( 'gutenberg/gutenberg.php' ) ) {
+	if ( ! empty( $theme_tags ) && in_array( 'full-site-editing', $theme_tags, true ) && ! function_exists( 'gutenberg_is_fse_theme' ) ) {
 		return new WP_Error(
 			'theme_requires_fse',
 			sprintf(