Index: Gruntfile.js
===================================================================
--- Gruntfile.js	(revision 46166)
+++ Gruntfile.js	(working copy)
@@ -303,7 +303,6 @@
 					[ WORKING_DIR + 'wp-includes/js/quicktags.js' ]: [ './src/js/_enqueues/lib/quicktags.js' ],
 					[ WORKING_DIR + 'wp-includes/js/shortcode.js' ]: [ './src/js/_enqueues/wp/shortcode.js' ],
 					[ WORKING_DIR + 'wp-includes/js/utils.js' ]: [ './src/js/_enqueues/lib/cookies.js' ],
-					[ WORKING_DIR + 'wp-includes/js/wp-a11y.js' ]: [ './src/js/_enqueues/wp/a11y.js' ],
 					[ WORKING_DIR + 'wp-includes/js/wp-ajax-response.js' ]: [ './src/js/_enqueues/lib/ajax-response.js' ],
 					[ WORKING_DIR + 'wp-includes/js/wp-api.js' ]: [ './src/js/_enqueues/wp/api.js' ],
 					[ WORKING_DIR + 'wp-includes/js/wp-auth-check.js' ]: [ './src/js/_enqueues/lib/auth-check.js' ],
@@ -846,7 +845,6 @@
 					'src/wp-includes/js/quicktags.js': 'src/js/_enqueues/lib/quicktags.js',
 					'src/wp-includes/js/shortcode.js': 'src/js/_enqueues/wp/shortcode.js',
 					'src/wp-includes/js/utils.js': 'src/js/_enqueues/lib/cookies.js',
-					'src/wp-includes/js/wp-a11y.js': 'src/js/_enqueues/wp/a11y.js',
 					'src/wp-includes/js/wp-ajax-response.js': 'src/js/_enqueues/lib/ajax-response.js',
 					'src/wp-includes/js/wp-api.js': 'src/js/_enqueues/wp/api.js',
 					'src/wp-includes/js/wp-auth-check.js': 'src/js/_enqueues/lib/auth-check.js',
Index: src/wp-admin/includes/update-core.php
===================================================================
--- src/wp-admin/includes/update-core.php	(revision 46166)
+++ src/wp-admin/includes/update-core.php	(working copy)
@@ -786,6 +786,9 @@
 	// 5.1
 	'wp-includes/random_compat/random_bytes_openssl.php',
 	'wp-includes/js/tinymce/wp-tinymce.js.gz',
+	// 5.3
+	'wp-includes/js/wp-a11y.js', // Moved to: wp-includes/js/dist/a11y.js
+	'wp-includes/js/wp-a11y.min.js', // Moved to: wp-includes/js/dist/a11y.min.js
 );
 
 /**
Index: tests/phpunit/tests/dependencies/scripts.php
===================================================================
--- tests/phpunit/tests/dependencies/scripts.php	(revision 46166)
+++ tests/phpunit/tests/dependencies/scripts.php	(working copy)
@@ -734,12 +734,12 @@
 		global $wp_scripts;
 
 		wp_default_scripts( $wp_scripts );
+		wp_default_packages( $wp_scripts );
 
 		$wp_scripts->base_url  = '';
 		$wp_scripts->do_concat = true;
 
-		$expected_tail  = "<![endif]-->\n";
-		$expected_tail .= "<script type='text/javascript' src='/customize-dependency.js'></script>\n";
+		$expected_tail = "<script type='text/javascript' src='/customize-dependency.js'></script>\n";
 		$expected_tail .= "<script type='text/javascript'>\n";
 		$expected_tail .= "tryCustomizeDependency()\n";
 		$expected_tail .= "</script>\n";
@@ -748,10 +748,12 @@
 		wp_enqueue_script( $handle, '/customize-dependency.js', array( 'customize-controls' ), null );
 		wp_add_inline_script( $handle, 'tryCustomizeDependency()' );
 
+		// Open a buffer to get the output of `wp_print_scripts`.
+		ob_start();
 		wp_print_scripts();
-		$print_scripts = get_echo( '_print_scripts' );
+		$print_scripts = ob_get_clean();
 
-		$tail = substr( $print_scripts, strrpos( $print_scripts, '<![endif]-->' ) );
+		$tail = substr( $print_scripts, strrpos( $print_scripts, "<script type='text/javascript' src='/customize-dependency.js'>" ) );
 		$this->assertEquals( $expected_tail, $tail );
 	}
 
Index: tests/qunit/index.html
===================================================================
--- tests/qunit/index.html	(revision 46166)
+++ tests/qunit/index.html	(working copy)
@@ -24,7 +24,7 @@
 			};
 		</script>
 		<script src="../../build/wp-includes/js/wp-util.js"></script>
-		<script src="../../build/wp-includes/js/wp-a11y.js"></script>
+		<script src="../../build/wp-includes/js/dist/a11y.js"></script>
 		<script>
 			window._wpMediaModelsL10n = {"settings":{"ajaxurl":"\/wp-admin\/admin-ajax.php","post":{"id":0}}};
 		</script>