diff --git a/build/update_stylesheet_querystrings.php b/build/update_stylesheet_querystrings.php
new file mode 100644
index 0000000000..e3a3f8de15
--- /dev/null
+++ b/build/update_stylesheet_querystrings.php
@@ -0,0 +1,54 @@
+<?php declare(strict_types=1);
+/**
+*
+* This file is part of the phpBB Forum Software package.
+*
+* @copyright (c) phpBB Limited <https://www.phpbb.com>
+* @license GNU General Public License, version 2 (GPL-2.0)
+*
+* For full copyright and license information, please see
+* the docs/CREDITS.txt file.
+*
+*/
+
+if (php_sapi_name() !== 'cli')
+{
+	die("This program must be run from the command line.\n");
+}
+
+if (version_compare(PHP_VERSION, '7.1.3', '<'))
+{
+	die('update_stylesheet_querystrings.php requires at least PHP 7.1.3');
+}
+
+// Usage: "$ php build/update_stylesheet_querystrings.php"
+$targets = [dirname(dirname(__FILE__)) . '/phpBB/styles/prosilver/theme/stylesheet.css'];
+
+array_map('patch_glob', $targets);
+
+function patch_glob($glob): void
+{
+	array_map('patch_file', glob($glob));
+}
+
+function patch_file(string $filepath): void
+{
+	$file	= file_get_contents($filepath);
+	$old	= $file;
+	$new	= preg_replace_callback(
+		'(^@import\\s+url\\([\'"](?<basename>\\w++\\.css)\\?\\K(?:hash|v)=[^\'"]++)m',
+		function ($match) use ($filepath)
+		{
+			$path = dirname($filepath) . DIRECTORY_SEPARATOR . $match['basename'];
+			$hash = sprintf('%08x', crc32(file_get_contents($path)));
+
+			return 'hash=' . $hash;
+		},
+		$old
+	);
+
+	if ($new !== $old)
+	{
+		file_put_contents($filepath, $new);
+	}
+}
diff --git a/phpBB/styles/prosilver/theme/stylesheet.css b/phpBB/styles/prosilver/theme/stylesheet.css
index c402d563c6..dd30ee42da 100644
--- a/phpBB/styles/prosilver/theme/stylesheet.css
+++ b/phpBB/styles/prosilver/theme/stylesheet.css
@@ -7,15 +7,15 @@
     --------------------------------------------------------------
 */
 
-@import url("normalize.css?v=3.3");
-@import url("base.css?v=3.3");
-@import url("utilities.css?v=3.3");
-@import url("common.css?v=3.3");
-@import url("links.css?v=3.3");
-@import url("content.css?v=3.3");
-@import url("buttons.css?v=3.3");
-@import url("cp.css?v=3.3");
-@import url("forms.css?v=3.3");
-@import url("icons.css?v=3.3");
-@import url("colours.css?v=3.3");
-@import url("responsive.css?v=3.3");
+@import url("normalize.css?hash=48eb3f89");
+@import url("base.css?hash=3a7fafb1");
+@import url("utilities.css?hash=1034bac8");
+@import url("common.css?hash=009a715d");
+@import url("links.css?hash=da040ebb");
+@import url("content.css?hash=d7d65e66");
+@import url("buttons.css?hash=15c14833");
+@import url("cp.css?hash=5cc9ac0c");
+@import url("forms.css?hash=18ee8211");
+@import url("icons.css?hash=ed93c566");
+@import url("colours.css?hash=3b03ccfa");
+@import url("responsive.css?hash=438ff202");