diff --git a/src/Core/Util/AdminHelpers.php b/src/Core/Util/AdminHelpers.php
index 85cb27c7..fcd16950 100644
--- a/src/Core/Util/AdminHelpers.php
+++ b/src/Core/Util/AdminHelpers.php
@@ -359,12 +359,14 @@ class AdminHelpers {
 	/**
 	 * Extract the page name (script basename) from a URL.
 	 *
-	 * @param string $rURL URL to parse.
-	 * @return string|null Lowercased page name, or null if $rURL is empty.
+	 * @param string|null $rURL URL to parse. post.php passes its optional
+	 *                          `referer` parameter, which the new-UI forms omit.
+	 * @return string|null Lowercased page name, or null if $rURL is empty or has no path.
 	 */
-	public static function getPageFromURL(string $rURL) {
-		if ($rURL) {
-			return strtolower(basename(ltrim(parse_url($rURL)['path'], '/'), '.php'));
+	public static function getPageFromURL(?string $rURL) {
+		$rPath = $rURL ? parse_url($rURL, PHP_URL_PATH) : null;
+		if (is_string($rPath) && trim($rPath, '/') !== '') {
+			return strtolower(basename(ltrim($rPath, '/'), '.php'));
 		}
 
 		return null;
diff --git a/tests/Unit/AdminHelpersTest.php b/tests/Unit/AdminHelpersTest.php
index fcefd5d5..b0f86f0a 100644
--- a/tests/Unit/AdminHelpersTest.php
+++ b/tests/Unit/AdminHelpersTest.php
@@ -64,6 +64,16 @@ final class AdminHelpersTest extends TestCase {
 		$this->assertNull(AdminHelpers::getPageFromURL(''));
 	}
 
+	/**
+	 * post.php hands over its `referer` parameter, which the new-UI forms do not
+	 * send: a null there must read as "no page", not end the request.
+	 */
+	public function testGetPageFromUrlWithoutAReferer() {
+		$this->assertNull(AdminHelpers::getPageFromURL(null));
+		$this->assertSame('lines', AdminHelpers::getPageFromURL('lines?status=1'));
+		$this->assertNull(AdminHelpers::getPageFromURL('http://host'));
+	}
+
 	public function testProtocolDetectionFromServerVars() {
 		$saved = $_SERVER;