diff --git a/packages/router/src/url_tree.ts b/packages/router/src/url_tree.ts
index e03cc058f0..ab99544b8c 100644
--- a/packages/router/src/url_tree.ts
+++ b/packages/router/src/url_tree.ts
@@ -115,7 +115,7 @@ export class UrlTree {
       /** The fragment of the URL */
       public fragment: string) {}
 
-  get queryParamMap() {
+  get queryParamMap(): ParamMap {
     if (!this._queryParamMap) {
       this._queryParamMap = convertToParamMap(this.queryParams);
     }
@@ -123,7 +123,7 @@ export class UrlTree {
   }
 
   /** @docsNotRequired */
-  toString(): string { return new DefaultUrlSerializer().serialize(this); }
+  toString(): string { return DEFAULT_SERIALIZER.serialize(this); }
 }
 
 /**
@@ -294,6 +294,8 @@ export class DefaultUrlSerializer implements UrlSerializer {
   }
 }
 
+const DEFAULT_SERIALIZER = new DefaultUrlSerializer();
+
 export function serializePaths(segment: UrlSegmentGroup): string {
   return segment.segments.map(p => serializePath(p)).join('/');
 }