diff --git a/projects/packages/jetpack-mu-wpcom/src/features/custom-css/custom-css/preprocessors.php b/projects/packages/jetpack-mu-wpcom/src/features/custom-css/custom-css/preprocessors.php
index ed8cdce97d282..ff08d68d5cb23 100644
--- a/projects/packages/jetpack-mu-wpcom/src/features/custom-css/custom-css/preprocessors.php
+++ b/projects/packages/jetpack-mu-wpcom/src/features/custom-css/custom-css/preprocessors.php
@@ -1,70 +1,76 @@
 <?php // phpcs:ignore WordPress.Files.FileName.InvalidClassFileName
 
-/**
- * CSS preprocessor registration.
- *
- * To add a new preprocessor (or replace an existing one), hook into the
- * jetpack_custom_css_preprocessors filter and add an entry to the array
- * that is passed in.
- *
- * Format is:
- * $preprocessors[ UNIQUE_KEY ] => array( 'name' => 'Processor name', 'callback' => [processing function] );
- *
- * The callback function accepts a single string argument (non-CSS markup) and returns a string (CSS).
- *
- * @param array $preprocessors The list of preprocessors added thus far.
- * @return array
- */
-function jetpack_register_css_preprocessors( $preprocessors ) {
-	$preprocessors['less'] = array(
-		'name'     => 'LESS',
-		'callback' => 'jetpack_less_css_preprocess',
-	);
+if ( ! function_exists( 'jetpack_register_css_preprocessors' ) ) {
+	/**
+	 * CSS preprocessor registration.
+	 *
+	 * To add a new preprocessor (or replace an existing one), hook into the
+	 * jetpack_custom_css_preprocessors filter and add an entry to the array
+	 * that is passed in.
+	 *
+	 * Format is:
+	 * $preprocessors[ UNIQUE_KEY ] => array( 'name' => 'Processor name', 'callback' => [processing function] );
+	 *
+	 * The callback function accepts a single string argument (non-CSS markup) and returns a string (CSS).
+	 *
+	 * @param array $preprocessors The list of preprocessors added thus far.
+	 * @return array
+	 */
+	function jetpack_register_css_preprocessors( $preprocessors ) {
+		$preprocessors['less'] = array(
+			'name'     => 'LESS',
+			'callback' => 'jetpack_less_css_preprocess',
+		);
 
-	$preprocessors['sass'] = array(
-		'name'     => 'Sass (SCSS Syntax)',
-		'callback' => 'jetpack_sass_css_preprocess',
-	);
+		$preprocessors['sass'] = array(
+			'name'     => 'Sass (SCSS Syntax)',
+			'callback' => 'jetpack_sass_css_preprocess',
+		);
 
-	return $preprocessors;
+		return $preprocessors;
+	}
 }
 
 add_filter( 'jetpack_custom_css_preprocessors', 'jetpack_register_css_preprocessors' );
 
-/**
- * Compile less prepocessors?
- *
- * @param string $less - less.
- */
-function jetpack_less_css_preprocess( $less ) {
-	require_once __DIR__ . '/preprocessors/lessc.inc.php';
+if ( ! function_exists( 'jetpack_less_css_preprocess' ) ) {
+	/**
+	 * Compile less prepocessors?
+	 *
+	 * @param string $less - less.
+	 */
+	function jetpack_less_css_preprocess( $less ) {
+		require_once __DIR__ . '/preprocessors/lessc.inc.php';
 
-	$compiler = new lessc();
+		$compiler = new lessc();
 
-	// Don't try to load from the filesystem.
-	$compiler->setImportDir( array() );
+		// Don't try to load from the filesystem.
+		$compiler->setImportDir( array() );
 
-	try {
-		return $compiler->compile( $less );
-	} catch ( Exception $e ) {
-		return $less;
+		try {
+			return $compiler->compile( $less );
+		} catch ( Exception $e ) {
+			return $less;
+		}
 	}
 }
 
-/**
- * Compile sass prepocessors?
- *
- * @param string $sass - sass.
- */
-function jetpack_sass_css_preprocess( $sass ) {
-	$compiler = new ScssPhp\ScssPhp\Compiler();
+if ( ! function_exists( 'jetpack_sass_css_preprocess' ) ) {
+	/**
+	 * Compile sass prepocessors?
+	 *
+	 * @param string $sass - sass.
+	 */
+	function jetpack_sass_css_preprocess( $sass ) {
+		$compiler = new ScssPhp\ScssPhp\Compiler();
 
-	// Don't try to load from the filesystem.
-	$compiler->setImportPaths( array() );
+		// Don't try to load from the filesystem.
+		$compiler->setImportPaths( array() );
 
-	try {
-		return $compiler->compileString( $sass )->getCss();
-	} catch ( Exception $e ) {
-		return $sass;
+		try {
+			return $compiler->compileString( $sass )->getCss();
+		} catch ( Exception $e ) {
+			return $sass;
+		}
 	}
 }
diff --git a/projects/plugins/jetpack/modules/custom-css/custom-css/preprocessors.php b/projects/plugins/jetpack/modules/custom-css/custom-css/preprocessors.php
index ed8cdce97d282..ff08d68d5cb23 100644
--- a/projects/plugins/jetpack/modules/custom-css/custom-css/preprocessors.php
+++ b/projects/plugins/jetpack/modules/custom-css/custom-css/preprocessors.php
@@ -1,70 +1,76 @@
 <?php // phpcs:ignore WordPress.Files.FileName.InvalidClassFileName
 
-/**
- * CSS preprocessor registration.
- *
- * To add a new preprocessor (or replace an existing one), hook into the
- * jetpack_custom_css_preprocessors filter and add an entry to the array
- * that is passed in.
- *
- * Format is:
- * $preprocessors[ UNIQUE_KEY ] => array( 'name' => 'Processor name', 'callback' => [processing function] );
- *
- * The callback function accepts a single string argument (non-CSS markup) and returns a string (CSS).
- *
- * @param array $preprocessors The list of preprocessors added thus far.
- * @return array
- */
-function jetpack_register_css_preprocessors( $preprocessors ) {
-	$preprocessors['less'] = array(
-		'name'     => 'LESS',
-		'callback' => 'jetpack_less_css_preprocess',
-	);
+if ( ! function_exists( 'jetpack_register_css_preprocessors' ) ) {
+	/**
+	 * CSS preprocessor registration.
+	 *
+	 * To add a new preprocessor (or replace an existing one), hook into the
+	 * jetpack_custom_css_preprocessors filter and add an entry to the array
+	 * that is passed in.
+	 *
+	 * Format is:
+	 * $preprocessors[ UNIQUE_KEY ] => array( 'name' => 'Processor name', 'callback' => [processing function] );
+	 *
+	 * The callback function accepts a single string argument (non-CSS markup) and returns a string (CSS).
+	 *
+	 * @param array $preprocessors The list of preprocessors added thus far.
+	 * @return array
+	 */
+	function jetpack_register_css_preprocessors( $preprocessors ) {
+		$preprocessors['less'] = array(
+			'name'     => 'LESS',
+			'callback' => 'jetpack_less_css_preprocess',
+		);
 
-	$preprocessors['sass'] = array(
-		'name'     => 'Sass (SCSS Syntax)',
-		'callback' => 'jetpack_sass_css_preprocess',
-	);
+		$preprocessors['sass'] = array(
+			'name'     => 'Sass (SCSS Syntax)',
+			'callback' => 'jetpack_sass_css_preprocess',
+		);
 
-	return $preprocessors;
+		return $preprocessors;
+	}
 }
 
 add_filter( 'jetpack_custom_css_preprocessors', 'jetpack_register_css_preprocessors' );
 
-/**
- * Compile less prepocessors?
- *
- * @param string $less - less.
- */
-function jetpack_less_css_preprocess( $less ) {
-	require_once __DIR__ . '/preprocessors/lessc.inc.php';
+if ( ! function_exists( 'jetpack_less_css_preprocess' ) ) {
+	/**
+	 * Compile less prepocessors?
+	 *
+	 * @param string $less - less.
+	 */
+	function jetpack_less_css_preprocess( $less ) {
+		require_once __DIR__ . '/preprocessors/lessc.inc.php';
 
-	$compiler = new lessc();
+		$compiler = new lessc();
 
-	// Don't try to load from the filesystem.
-	$compiler->setImportDir( array() );
+		// Don't try to load from the filesystem.
+		$compiler->setImportDir( array() );
 
-	try {
-		return $compiler->compile( $less );
-	} catch ( Exception $e ) {
-		return $less;
+		try {
+			return $compiler->compile( $less );
+		} catch ( Exception $e ) {
+			return $less;
+		}
 	}
 }
 
-/**
- * Compile sass prepocessors?
- *
- * @param string $sass - sass.
- */
-function jetpack_sass_css_preprocess( $sass ) {
-	$compiler = new ScssPhp\ScssPhp\Compiler();
+if ( ! function_exists( 'jetpack_sass_css_preprocess' ) ) {
+	/**
+	 * Compile sass prepocessors?
+	 *
+	 * @param string $sass - sass.
+	 */
+	function jetpack_sass_css_preprocess( $sass ) {
+		$compiler = new ScssPhp\ScssPhp\Compiler();
 
-	// Don't try to load from the filesystem.
-	$compiler->setImportPaths( array() );
+		// Don't try to load from the filesystem.
+		$compiler->setImportPaths( array() );
 
-	try {
-		return $compiler->compileString( $sass )->getCss();
-	} catch ( Exception $e ) {
-		return $sass;
+		try {
+			return $compiler->compileString( $sass )->getCss();
+		} catch ( Exception $e ) {
+			return $sass;
+		}
 	}
 }