diff --git a/src/app/pages/error/valid-code.guard.ts b/src/app/pages/error/valid-code.guard.ts
index 70d3197..c460f73 100644
--- a/src/app/pages/error/valid-code.guard.ts
+++ b/src/app/pages/error/valid-code.guard.ts
@@ -20,7 +20,7 @@ export class ValidCodeGuard implements CanActivate {
      */
     public canActivate(route: ActivatedRouteSnapshot): boolean | UrlTree {
         // show empty error page if no code is present
-        if (route?.queryParamMap?.has('code') ?? false) {
+        if (!(route?.queryParamMap?.has('code') ?? false)) {
             return true
         }
 
@@ -28,17 +28,12 @@ export class ValidCodeGuard implements CanActivate {
         if (!/^\d{3}$/.test(route?.queryParamMap?.get('code') ?? '')) {
             console.info(`No valid error code found, redirecting to ${StatusCodes.NOT_FOUND}.`)
 
-            // prepare retry url
-            const retry = new URL(this.document.location?.href ?? '')
-            retry.searchParams.delete('code')
-            retry.searchParams.delete('retry')
-
             // redirect to 404 if not valid
-            return this.router.createUrlTree([this.document.location?.pathname ?? '/'], {
+            return this.router.createUrlTree([this.document?.location?.pathname ?? '/'], {
                 queryParams: {
                     code: StatusCodes.NOT_FOUND,
                     home: route?.queryParams.home,
-                    retry: retry.toString(),
+                    retry: this.buildRetryUrl(),
                 },
             })
         }
@@ -46,4 +41,22 @@ export class ValidCodeGuard implements CanActivate {
         // show error page for code parameter
         return true
     }
+
+    /**
+     * Tries to build a retry URL from the current location href.
+     *
+     * @returns Returns the retry URL string or null.
+     */
+    private buildRetryUrl(): string | null {
+        if (this.document?.location?.href?.length === 0) {
+            return null
+        }
+
+        // remove code and retry parameters to prevent infinite loop
+        const retry = new URL(this.document?.location?.href ?? '')
+        retry.searchParams.delete('code')
+        retry.searchParams.delete('retry')
+
+        return retry.toString()
+    }
 }