diff --git a/lib/url_hack.ts b/lib/url_hack.ts
index bed28e27..38051cba 100644
--- a/lib/url_hack.ts
+++ b/lib/url_hack.ts
@@ -1,48 +1,82 @@
-export const urlPrefix: string = Deno.env.get("SB_URL_PREFIX") ??
-  (globalThis.silverBulletConfig
-    ? globalThis.silverBulletConfig.urlPrefix
-    : null) ??
-  "";
-
-export const toRealUrl = <T extends (string | URL)>(url: T): T => {
-  if (typeof url === "string") {
-    const stringUrl = url as string;
-    if (stringUrl.startsWith("http://") || stringUrl.startsWith("https://")) {
-      const parsedUrl = new URL(stringUrl);
-      parsedUrl.pathname = urlPrefix + parsedUrl.pathname;
-      //console.log("Converted ", url, parsedUrl.href)
-      return String(parsedUrl.href) as T;
-    } else {
-      if (!stringUrl.startsWith("/")) {
-        console.log("Don't know how to deal with relative path: ", url);
-      }
-      //console.log("Converted ", url, urlPrefix + stringUrl)
-      return (urlPrefix + stringUrl) as T;
+const getUrlPrefix = () : string => {
+    const prefix : string = Deno.env.get("SB_URL_PREFIX") ??
+      (globalThis.silverBulletConfig ?
+       globalThis.silverBulletConfig.urlPrefix
+       : null) ?? '';
+    if (prefix === '') {
+        return '';
     }
-  } else if (url.protocol === "http:" || url.protocol === "https:") {
-    const parsedUrl = new URL(url as URL);
-    parsedUrl.pathname = urlPrefix + parsedUrl.pathname;
-    //console.log("Converted ", url, parsedUrl)
-    return parsedUrl as T;
-  } else {
-    return url;
-  }
+
+    let result = prefix;
+    if (!prefix.startsWith('/')) {
+        result = '/' + result;
+    }
+    if (prefix.endsWith('/')) {
+        result = result.replace(/\/*$/, '');
+    }
+
+    return result;
 };
 
-export const toInternalUrl = (url: string) => {
-  if (url.startsWith("http://") || url.startsWith("https://")) {
+export const urlPrefix: string = getUrlPrefix();
+
+const toRealUrlObject = (url : URL) : URL => {
     const parsedUrl = new URL(url);
-    if (parsedUrl.pathname.startsWith(urlPrefix)) {
-      parsedUrl.pathname = parsedUrl.pathname.substr(urlPrefix.length);
-      return parsedUrl.href;
+    if (typeof location !== 'undefined' && parsedUrl.origin == location.origin) {
+        if (parsedUrl.pathname.startsWith(urlPrefix)) {
+            //console.trace("Path starts with prefix already: ", url);
+        }
+
+        parsedUrl.pathname = urlPrefix + parsedUrl.pathname;
+        //console.trace("Converted full URL ", url, parsedUrl.href)
+        return parsedUrl;
     } else {
-      console.log("Don't know how to deal with non-prefix: ", url);
-      return url;
+        //console.trace("Don't know how to deal with cross origin path: ", url);
+        return url;
+    }
+}
+
+export const toRealUrl = <T extends (string | URL)>(url : T) : T => {
+    if (typeof url === 'string') {
+        const stringUrl = url as string;
+        if (stringUrl.startsWith('http://') || stringUrl.startsWith('https://')) {
+            return toRealUrlObject(new URL(stringUrl)).href as T;
+        }
+        else if (!stringUrl.startsWith('/')) {
+            //console.trace("Don't know how to deal with relative path: ", url);
+            return url;
+        } else {
+            if (url.startsWith(urlPrefix)) {
+                //console.trace("Path starts with prefix already: ", url);
+            }
+            //console.trace("Converted absolute path ", url, urlPrefix + stringUrl)
+            return (urlPrefix + stringUrl) as T;
+        }
+    }
+    else if (url.protocol === 'http:' || url.protocol === 'https:') {
+        return toRealUrlObject(url) as T;
+    }
+    else {
+        return url;
+    }
+};
+
+export const toInternalUrl = (url : string) => {
+    if (url.startsWith('http://') || url.startsWith('https://')) {
+        const parsedUrl = new URL(url);
+        if (parsedUrl.pathname.startsWith(urlPrefix)) {
+            parsedUrl.pathname = parsedUrl.pathname.substr(urlPrefix.length);
+            return parsedUrl.href;
+        }
+        else {
+            //console.trace("Don't know how to deal with non-prefix: ", url);
+            return url;
+        }
+    } else if (url.startsWith(urlPrefix)) {
+        return url.substr(urlPrefix.length);
+    }
+    else {
+        //console.trace("Don't know how to deal with non-prefix: ", url);
+        return url;
     }
-  } else if (url.startsWith(urlPrefix)) {
-    return url.substr(urlPrefix.length);
-  } else {
-    console.log("Don't know how to deal with non-prefix: ", url);
-    return url;
-  }
 };
diff --git a/server/http_server.ts b/server/http_server.ts
index 46cbbe98..e0cdbf8a 100644
--- a/server/http_server.ts
+++ b/server/http_server.ts
@@ -404,13 +404,14 @@ export class HttpServer {
         return next();
       }
       const url = new URL(toInternalUrl(req.url));
+      const path = toInternalUrl(req.path);
       const host = url.host;
       const redirectToAuth = () => {
         // Try filtering api paths
-        if (req.path.startsWith("/.") || req.path.endsWith(".md")) {
+        if (path.startsWith("/.") || path.endsWith(".md")) {
           return c.redirect(toRealUrl("/.auth"), 401);
         } else {
-          return c.redirect(toRealUrl(`/.auth?from=${req.path}`), 401);
+          return c.redirect(toRealUrl(`/.auth?from=${path}`), 401);
         }
       };
       if (!excludedPaths.includes(url.pathname)) {
diff --git a/web/boot.ts b/web/boot.ts
index 16718b10..f5b48386 100644
--- a/web/boot.ts
+++ b/web/boot.ts
@@ -1,5 +1,6 @@
 import { safeRun } from "../lib/async.ts";
 import { Client } from "./client.ts";
+import { toRealUrl } from "../lib/url_hack.ts";
 
 const syncMode = globalThis.silverBulletConfig.syncOnly ||
   !!localStorage.getItem("syncMode");
@@ -26,7 +27,7 @@ safeRun(async () => {
 
 if (navigator.serviceWorker) {
   navigator.serviceWorker
-    .register(new URL("/service_worker.js", location.href), {
+    .register(new URL(toRealUrl("/service_worker.js"), location.href), {
       type: "module",
     })
     .then(() => {