diff --git a/wp-includes/compat.php b/wp-includes/compat.php
index 0ccee2d498..7e37c30762 100644
--- a/wp-includes/compat.php
+++ b/wp-includes/compat.php
@@ -488,93 +488,12 @@ if ( ! function_exists( 'array_replace_recursive' ) ) :
 	}
 endif;
 
-// SPL can be disabled on PHP 5.2
-if ( ! function_exists( 'spl_autoload_register' ) ):
-	$_wp_spl_autoloaders = array();
-
-	/**
-	 * Autoloader compatibility callback.
-	 *
-	 * @since 4.6.0
-	 *
-	 * @param string $classname Class to attempt autoloading.
-	 */
-	function __autoload( $classname ) {
-		global $_wp_spl_autoloaders;
-		foreach ( $_wp_spl_autoloaders as $autoloader ) {
-			if ( ! is_callable( $autoloader ) ) {
-				// Avoid the extra warning if the autoloader isn't callable.
-				continue;
-			}
-
-			call_user_func( $autoloader, $classname );
-
-			// If it has been autoloaded, stop processing.
-			if ( class_exists( $classname, false ) ) {
-				return;
-			}
-		}
-	}
-
-	/**
-	 * Registers a function to be autoloaded.
-	 *
-	 * @since 4.6.0
-	 *
-	 * @param callable $autoload_function The function to register.
-	 * @param bool     $throw             Optional. Whether the function should throw an exception
-	 *                                    if the function isn't callable. Default true.
-	 * @param bool     $prepend           Whether the function should be prepended to the stack.
-	 *                                    Default false.
-	 */
-	function spl_autoload_register( $autoload_function, $throw = true, $prepend = false ) {
-		if ( $throw && ! is_callable( $autoload_function ) ) {
-			// String not translated to match PHP core.
-			throw new Exception( 'Function not callable' );
-		}
-
-		global $_wp_spl_autoloaders;
-
-		// Don't allow multiple registration.
-		if ( in_array( $autoload_function, $_wp_spl_autoloaders ) ) {
-			return;
-		}
-
-		if ( $prepend ) {
-			array_unshift( $_wp_spl_autoloaders, $autoload_function );
-		} else {
-			$_wp_spl_autoloaders[] = $autoload_function;
-		}
-	}
-
-	/**
-	 * Unregisters an autoloader function.
-	 *
-	 * @since 4.6.0
-	 *
-	 * @param callable $function The function to unregister.
-	 * @return bool True if the function was unregistered, false if it could not be.
-	 */
-	function spl_autoload_unregister( $function ) {
-		global $_wp_spl_autoloaders;
-		foreach ( $_wp_spl_autoloaders as &$autoloader ) {
-			if ( $autoloader === $function ) {
-				unset( $autoloader );
-				return true;
-			}
-		}
-
-		return false;
-	}
-
-	/**
-	 * Retrieves the registered autoloader functions.
-	 *
-	 * @since 4.6.0
-	 *
-	 * @return array List of autoloader functions.
-	 */
-	function spl_autoload_functions() {
-		return $GLOBALS['_wp_spl_autoloaders'];
-	}
-endif;
+/**
+ * Polyfill for the SPL autoloader. In PHP 5.2 (but not 5.3 and later), SPL can
+ * be disabled, and PHP 7.2 raises notices if the compiler finds an __autoload()
+ * function declaration. Function availability is checked here, and the
+ * autoloader is included only if necessary.
+ */
+if ( ! function_exists( 'spl_autoload_register' ) ) {
+	require_once ABSPATH . WPINC . '/spl-autoload-compat.php';
+}
diff --git a/wp-includes/spl-autoload-compat.php b/wp-includes/spl-autoload-compat.php
new file mode 100644
index 0000000000..599b6046b3
--- /dev/null
+++ b/wp-includes/spl-autoload-compat.php
@@ -0,0 +1,100 @@
+<?php
+/**
+ * Polyfill for SPL autoload feature. This file is separate to prevent compiler notices
+ * on the deprecated __autoload() function.
+ *
+ * See https://core.trac.wordpress.org/ticket/41134
+ *
+ * @package PHP
+ * @access private
+ */
+
+if ( ! function_exists( 'spl_autoload_register' ) ) {
+	$_wp_spl_autoloaders = array();
+
+	/**
+	 * Autoloader compatibility callback.
+	 *
+	 * @since 4.6.0
+	 *
+	 * @param string $classname Class to attempt autoloading.
+	 */
+	function __autoload( $classname ) {
+		global $_wp_spl_autoloaders;
+		foreach ( $_wp_spl_autoloaders as $autoloader ) {
+			if ( ! is_callable( $autoloader ) ) {
+				// Avoid the extra warning if the autoloader isn't callable.
+				continue;
+			}
+
+			call_user_func( $autoloader, $classname );
+
+			// If it has been autoloaded, stop processing.
+			if ( class_exists( $classname, false ) ) {
+				return;
+			}
+		}
+	}
+
+	/**
+	 * Registers a function to be autoloaded.
+	 *
+	 * @since 4.6.0
+	 *
+	 * @param callable $autoload_function The function to register.
+	 * @param bool     $throw             Optional. Whether the function should throw an exception
+	 *                                    if the function isn't callable. Default true.
+	 * @param bool     $prepend           Whether the function should be prepended to the stack.
+	 *                                    Default false.
+	 */
+	function spl_autoload_register( $autoload_function, $throw = true, $prepend = false ) {
+		if ( $throw && ! is_callable( $autoload_function ) ) {
+			// String not translated to match PHP core.
+			throw new Exception( 'Function not callable' );
+		}
+
+		global $_wp_spl_autoloaders;
+
+		// Don't allow multiple registration.
+		if ( in_array( $autoload_function, $_wp_spl_autoloaders ) ) {
+			return;
+		}
+
+		if ( $prepend ) {
+			array_unshift( $_wp_spl_autoloaders, $autoload_function );
+		} else {
+			$_wp_spl_autoloaders[] = $autoload_function;
+		}
+	}
+
+	/**
+	 * Unregisters an autoloader function.
+	 *
+	 * @since 4.6.0
+	 *
+	 * @param callable $function The function to unregister.
+	 * @return bool True if the function was unregistered, false if it could not be.
+	 */
+	function spl_autoload_unregister( $function ) {
+		global $_wp_spl_autoloaders;
+		foreach ( $_wp_spl_autoloaders as &$autoloader ) {
+			if ( $autoloader === $function ) {
+				unset( $autoloader );
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	/**
+	 * Retrieves the registered autoloader functions.
+	 *
+	 * @since 4.6.0
+	 *
+	 * @return array List of autoloader functions.
+	 */
+	function spl_autoload_functions() {
+		return $GLOBALS['_wp_spl_autoloaders'];
+	}
+}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 3f93447772..a705ce846b 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-alpha-41177';
+$wp_version = '4.9-alpha-41178';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.