diff --git a/cli/js/url.ts b/cli/js/url.ts
index 7b06fd64c8..e5cf3ed623 100644
--- a/cli/js/url.ts
+++ b/cli/js/url.ts
@@ -17,7 +17,7 @@ interface URLParts {
 }
 
 const patterns = {
-  protocol: "(?:([^:/?#]+):)",
+  protocol: "(?:([a-z]+):)",
   authority: "(?://([^/?#]*))",
   path: "([^?#]*)",
   query: "(\\?[^#]*)",
@@ -228,10 +228,13 @@ export class URL {
       this.username || this.password
         ? `${this.username}${this.password ? ":" + this.password : ""}@`
         : "";
-
-    return `${this.protocol}//${authentication}${this.host}${this.pathname}${
-      this.search
-    }${this.hash}`;
+    let slash = "";
+    if (this.host || this.protocol === "file:") {
+      slash = "//";
+    }
+    return `${this.protocol}${slash}${authentication}${this.host}${
+      this.pathname
+    }${this.search}${this.hash}`;
   }
 
   set href(value: string) {
@@ -244,7 +247,10 @@ export class URL {
   }
 
   get origin(): string {
-    return `${this.protocol}//${this.host}`;
+    if (this.host) {
+      return `${this.protocol}//${this.host}`;
+    }
+    return "null";
   }
 
   get password(): string {
diff --git a/cli/js/url_test.ts b/cli/js/url_test.ts
index 23f9f5f4b0..1f8e319997 100644
--- a/cli/js/url_test.ts
+++ b/cli/js/url_test.ts
@@ -1,5 +1,5 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import { test, assert, assertEquals } from "./test_util.ts";
+import { test, assert, assertEquals, assertThrows } from "./test_util.ts";
 
 test(function urlParsing(): void {
   const url = new URL(
@@ -187,3 +187,16 @@ test(function customInspectFunction(): void {
     'URL { href: "http://example.com/?", origin: "http://example.com", protocol: "http:", username: "", password: "", host: "example.com", hostname: "example.com", port: "", pathname: "/", hash: "", search: "?" }'
   );
 });
+
+test(function protocolNotHttpOrFile() {
+  const url = new URL("about:blank");
+  assertEquals(url.href, "about:blank");
+  assertEquals(url.protocol, "about:");
+  assertEquals(url.origin, "null");
+});
+
+test(function createBadUrl(): void {
+  assertThrows(() => {
+    new URL("0.0.0.0:8080");
+  });
+});