diff --git a/src/pyodide.js b/src/pyodide.js
index 25691ffd6..c2f1050a9 100644
--- a/src/pyodide.js
+++ b/src/pyodide.js
@@ -3,7 +3,7 @@
  */
 
 // Regexp for validating package name and URI
-var package_name_regexp = '[a-z0-9_\-]+'
+var package_name_regexp = '[a-z0-9_][a-z0-9_\-]*'
 var package_uri_regexp =
     new RegExp('^https?://.*?(' + package_name_regexp + ').js$', 'i');
 var package_name_regexp = new RegExp('^' + package_name_regexp + '$', 'i');
@@ -44,8 +44,7 @@ var languagePluginLoader = new Promise((resolve, reject) => {
       const package = _uri_to_package_name(package_uri);
 
       if (package == null) {
-        console.log(`Invalid package name or URI '${package_uri}'`);
-        break;
+        throw new Error(`Invalid package name or URI '${package_uri}'`);
       } else if (package == package_uri) {
         package_uri = 'default channel';
       }
@@ -54,9 +53,10 @@ var languagePluginLoader = new Promise((resolve, reject) => {
 
       if (package in loadedPackages) {
         if (package_uri != loadedPackages[package]) {
-          console.log(`Error: URI mismatch, attempting to load package ` +
-                      `${package} from ${package_uri} while it is already ` +
-                      `loaded from ${loadedPackages[package]}!`);
+          throw new Error(
+              `URI mismatch, attempting to load package ` +
+              `${package} from ${package_uri} while it is already ` +
+              `loaded from ${loadedPackages[package]}!`);
         }
       } else {
         toLoad[package] = package_uri;
@@ -67,7 +67,7 @@ var languagePluginLoader = new Promise((resolve, reject) => {
             }
           });
         } else {
-          console.log(`Unknown package '${package}'`);
+          log.console(`Unknown package '${package}'`);
         }
       }
     }
diff --git a/test/conftest.py b/test/conftest.py
index 7d988ede0..9abca9395 100644
--- a/test/conftest.py
+++ b/test/conftest.py
@@ -40,7 +40,8 @@ def _display_driver_logs(browser, driver):
     elif browser == 'firefox':
         # browser logs are not available in GeckoDriver
         # https://github.com/mozilla/geckodriver/issues/284
-        print('Cannot access browser logs for Firefox.')
+        print('Accessing raw browser logs with Selenium is not '
+              'supported by Firefox.')
 
 
 class SeleniumWrapper:
diff --git a/test/test_package_loading.py b/test/test_package_loading.py
index 52f0d8338..47e87d3df 100644
--- a/test/test_package_loading.py
+++ b/test/test_package_loading.py
@@ -1,3 +1,5 @@
+import pytest
+from selenium.common.exceptions import WebDriverException
 
 
 def test_load_from_url(selenium_standalone, web_server):
@@ -16,15 +18,19 @@ def test_load_from_url(selenium_standalone, web_server):
 
 def test_uri_mismatch(selenium_standalone):
     selenium_standalone.load_package('pyparsing')
-    selenium_standalone.load_package('http://some_url/pyparsing.js')
+    with pytest.raises(WebDriverException,
+                       match="URI mismatch, attempting "
+                             "to load package pyparsing"):
+        selenium_standalone.load_package('http://some_url/pyparsing.js')
     assert "Invalid package name or URI" not in selenium_standalone.logs
-    assert ("URI mismatch, attempting "
-            "to load package pyparsing") in selenium_standalone.logs
 
 
 def test_invalid_package_name(selenium):
-    selenium.load_package('wrong name+$')
-    assert "Invalid package name or URI" in selenium.logs
+    with pytest.raises(WebDriverException,
+                       match="Invalid package name or URI"):
+        selenium.load_package('wrong name+$')
     selenium.clean_logs()
-    selenium.load_package('tcp://some_url')
-    assert "Invalid package name or URI" in selenium.logs
+
+    with pytest.raises(WebDriverException,
+                       match="Invalid package name or URI"):
+        selenium.load_package('tcp://some_url')