diff --git a/packages/meteor/url_server.js b/packages/meteor/url_server.js
index 81b55e776f..9eee42f0c3 100644
--- a/packages/meteor/url_server.js
+++ b/packages/meteor/url_server.js
@@ -1,6 +1,15 @@
 if (process.env.ROOT_URL &&
     typeof __meteor_runtime_config__ === "object") {
   __meteor_runtime_config__.ROOT_URL = process.env.ROOT_URL;
-  var pathPrefix = Npm.require('url').parse(__meteor_runtime_config__.ROOT_URL).pathname;
-  __meteor_runtime_config__.ROOT_URL_PATH_PREFIX = pathPrefix === "/" ? "" : pathPrefix;
+  if (__meteor_runtime_config__.ROOT_URL) {
+    var parsedUrl = Npm.require('url').parse(__meteor_runtime_config__.ROOT_URL);
+    // Sometimes users try to pass, eg, ROOT_URL=mydomain.com.
+    if (!parsedUrl.host) {
+      throw Error("$ROOT_URL, if specified, must be an URL");
+    }
+    var pathPrefix = parsedUrl.pathname;
+    __meteor_runtime_config__.ROOT_URL_PATH_PREFIX = pathPrefix === "/" ? "" : pathPrefix;
+  } else {
+    __meteor_runtime_config__.ROOT_URL_PATH_PREFIX = "";
+  }
 }
diff --git a/tools/main.js b/tools/main.js
index 5ec8a8622b..4521e2b9f5 100644
--- a/tools/main.js
+++ b/tools/main.js
@@ -337,6 +337,17 @@ Fiber(function () {
     process.exit(1);
   }
 
+  // This is a bit of a hack, but: if we don't check this in the tool, then the
+  // first time we do a unipackage.load, it will fail due to the check in the
+  // meteor package, and that'll look a lot uglier.
+  if (process.env.ROOT_URL) {
+    var parsedUrl = require('url').parse(process.env.ROOT_URL);
+    if (!parsedUrl.host) {
+      process.stderr.write('$ROOT_URL, if specified, must be an URL.\n');
+      process.exit(1);
+    }
+  }
+
   // Parse the arguments.
   //
   // We must first identify which options are boolean and which take