diff --git a/src/URLFixer.php b/src/URLFixer.php
index cb88f1b..d5ee270 100644
--- a/src/URLFixer.php
+++ b/src/URLFixer.php
@@ -13,20 +13,34 @@ class URLFixer
     /**
      * Add filters to verify / fix URLs.
      */
-    public function addFilters()
+    public function addFilters(): void
     {
+        // Do not interfere while network admin is processing a form submission.
+        // This prevents the filters from corrupting the values being saved.
+        if ($this->isSavingContext()) {
+            return;
+        }
+
         add_filter('option_home', [$this, 'fixHomeURL']);
         add_filter('option_siteurl', [$this, 'fixSiteURL']);
         add_filter('network_site_url', [$this, 'fixNetworkSiteURL'], 10, 3);
     }
 
+    /**
+     * Whether we are currently saving options in the network admin.
+     */
+    protected function isSavingContext(): bool
+    {
+        return is_admin() && is_network_admin() && $_SERVER['REQUEST_METHOD'] === 'POST';
+    }
+
     /**
      * Ensure that home URL does not contain the /wp subdirectory.
      *
      * @param string $value the unchecked home URL
      * @return string the verified home URL
      */
-    public function fixHomeURL($value)
+    public function fixHomeURL(string $value): string
     {
         if (substr($value, -3) === '/wp') {
             $value = substr($value, 0, -3);
@@ -40,7 +54,7 @@ public function fixHomeURL($value)
      * @param string $url the unchecked site URL
      * @return string the verified site URL
      */
-    public function fixSiteURL($url)
+    public function fixSiteURL(string $url): string
     {
         if (substr($url, -3) !== '/wp' && (is_main_site() || is_subdomain_install())) {
             $url .= '/wp';
@@ -56,7 +70,7 @@ public function fixSiteURL($url)
      * @param string $scheme the URL scheme
      * @return string the verified network site URL
      */
-    public function fixNetworkSiteURL($url, $path, $scheme)
+    public function fixNetworkSiteURL(string $url, string $path, string $scheme): string
     {
         $path = ltrim($path, '/');
         $url = substr($url, 0, strlen($url) - strlen($path));