diff --git a/cli/src/native/network.rs b/cli/src/native/network.rs
index 0f178d7b..48226e2a 100644
--- a/cli/src/native/network.rs
+++ b/cli/src/native/network.rs
@@ -184,7 +184,7 @@ pub async fn install_domain_filter_script(
             const OrigWS = window.WebSocket;
             window.WebSocket = function(url, protocols) {{
                 try {{
-                    const u = new URL(url);
+                    const u = new URL(url, location.href);
                     if (!_isDomainAllowed(u.hostname)) throw new DOMException('WebSocket blocked: ' + u.hostname, 'SecurityError');
                 }} catch(e) {{ if (e instanceof DOMException) throw e; }}
                 return new OrigWS(url, protocols);
diff --git a/src/domain-filter.ts b/src/domain-filter.ts
index 19dbff8a..77749921 100644
--- a/src/domain-filter.ts
+++ b/src/domain-filter.ts
@@ -51,7 +51,8 @@ export function buildWebSocketFilterScript(allowedDomains: string[]): string {
   }
   function _checkUrl(url) {
     try {
-      var parsed = new URL(url);
+      // Resolve relative URLs against current page origin (e.g., /__webpack_hmr)
+      var parsed = new URL(url, location.href);
       return _isDomainAllowed(parsed.hostname);
     } catch(e) {
       return false;