diff --git a/src/Admin/PackageManagerPage.php b/src/Admin/PackageManagerPage.php
index d95038a..c0cee86 100644
--- a/src/Admin/PackageManagerPage.php
+++ b/src/Admin/PackageManagerPage.php
@@ -14,7 +14,7 @@ final class PackageManagerPage
     private const string ACTION_QUERY_VAR = 'kernel-package-action';
     private const string PACKAGE_QUERY_VAR = 'kernel-package';
     private const string NOTICE_QUERY_VAR = 'kernel-package-notice';
-    private const string MESSAGE_QUERY_VAR = 'kernel-package-message';
+    private const string NOTICE_TRANSIENT_PREFIX = 'kernel_package_notice_';
     private const string VIEW_QUERY_VAR = 'package_status';
     private const string BULK_NONCE_ACTION = 'bulk-packages';
 
@@ -186,7 +186,7 @@ public function render(): void
         $packages = $this->packages->all();
         $currentView = $this->currentView();
         $notice = $this->requestString(self::NOTICE_QUERY_VAR);
-        $message = $this->noticeMessage($notice, $this->requestString(self::MESSAGE_QUERY_VAR));
+        $message = $notice === '' ? '' : $this->noticeMessage($notice, $this->takeNoticeMessage());
 
         $this->view($currentView, $notice, $message)->render(
             $packages,
@@ -400,23 +400,49 @@ private function nonceAction(string $action, PackageMetadata $package): string
 
     private function redirect(string $notice, string $message = ''): never
     {
+        // Free text never travels through the URL: a crafted link could otherwise
+        // show an administrator an arbitrary notice.
+        $this->stashNoticeMessage($message);
         wp_safe_redirect(
             $this->pageUrl(
-                array_filter(
-                    array_merge(
-                        $this->currentViewArgs(),
-                        [
-                            self::NOTICE_QUERY_VAR  => $notice,
-                            self::MESSAGE_QUERY_VAR => $message,
-                        ],
-                    ),
-                    static fn (string $value): bool => $value !== '',
-                ),
+                array_merge($this->currentViewArgs(), [self::NOTICE_QUERY_VAR => $notice]),
             ),
         );
         exit;
     }
 
+    private function stashNoticeMessage(string $message): void
+    {
+        if ($message === '' || !function_exists('set_transient')) {
+            return;
+        }
+
+        set_transient($this->noticeTransientKey(), $message, 60);
+    }
+
+    private function takeNoticeMessage(): string
+    {
+        if (!function_exists('get_transient')) {
+            return '';
+        }
+
+        $key = $this->noticeTransientKey();
+        $message = get_transient($key);
+
+        if ($message !== false) {
+            delete_transient($key);
+        }
+
+        return is_string($message) ? $message : '';
+    }
+
+    private function noticeTransientKey(): string
+    {
+        $user = function_exists('get_current_user_id') ? get_current_user_id() : 0;
+
+        return self::NOTICE_TRANSIENT_PREFIX . $user;
+    }
+
     private function isPostRequest(): bool
     {
         return ($_SERVER['REQUEST_METHOD'] ?? '') === 'POST';
diff --git a/tests/Admin/PackageManagerPageTest.php b/tests/Admin/PackageManagerPageTest.php
index a1afb85..ffa3725 100644
--- a/tests/Admin/PackageManagerPageTest.php
+++ b/tests/Admin/PackageManagerPageTest.php
@@ -133,6 +133,38 @@ function wp_clean_plugins_cache(bool $clearUpdateCache = true): void
             $GLOBALS['kernel_test_plugins_cache_cleaned'] = $clearUpdateCache;
         }
     }
+
+    if (!function_exists('get_current_user_id')) {
+        function get_current_user_id(): int
+        {
+            return 7;
+        }
+    }
+
+    if (!function_exists('set_transient')) {
+        function set_transient(string $transient, mixed $value, int $expiration = 0): bool
+        {
+            $GLOBALS['kernel_test_transients'][$transient] = $value;
+
+            return true;
+        }
+    }
+
+    if (!function_exists('get_transient')) {
+        function get_transient(string $transient): mixed
+        {
+            return $GLOBALS['kernel_test_transients'][$transient] ?? false;
+        }
+    }
+
+    if (!function_exists('delete_transient')) {
+        function delete_transient(string $transient): bool
+        {
+            unset($GLOBALS['kernel_test_transients'][$transient]);
+
+            return true;
+        }
+    }
 }
 
 namespace SymPress\Kernel\Tests\Admin {
@@ -199,6 +231,24 @@ public function testPackageManagerRegistersAdminPageWhenEnabled(): void
             );
         }
 
+        public function testNoticeMessagesTravelThroughAUserTransientNotTheUrl(): void
+        {
+            $GLOBALS['kernel_test_transients'] = [];
+            $_GET['kernel-package-message'] = 'Crafted link text';
+
+            try {
+                $this->invokePageMethod('stashNoticeMessage', 'Package not found.');
+
+                self::assertSame(['kernel_package_notice_7' => 'Package not found.'], $GLOBALS['kernel_test_transients']);
+                self::assertSame('Package not found.', $this->invokePageMethod('takeNoticeMessage'));
+                self::assertSame([], $GLOBALS['kernel_test_transients']);
+                self::assertSame('', $this->invokePageMethod('takeNoticeMessage'));
+                self::assertSame('Package action failed.', $this->invokePageMethod('noticeMessage', 'error', ''));
+            } finally {
+                unset($GLOBALS['kernel_test_transients'], $_GET['kernel-package-message']);
+            }
+        }
+
         public function testActionsAreBlockedWhenWordPressDisallowsFileModifications(): void
         {
             $GLOBALS['kernel_test_file_mod_allowed']['plugins'] = false;