diff --git a/okhttp/src/main/java/com/squareup/okhttp/internal/Dns.java b/okhttp/src/main/java/com/squareup/okhttp/internal/Dns.java
index 69b2d37e9..a89b293c0 100644
--- a/okhttp/src/main/java/com/squareup/okhttp/internal/Dns.java
+++ b/okhttp/src/main/java/com/squareup/okhttp/internal/Dns.java
@@ -25,6 +25,7 @@ import java.net.UnknownHostException;
 public interface Dns {
   Dns DEFAULT = new Dns() {
     @Override public InetAddress[] getAllByName(String host) throws UnknownHostException {
+      if (host == null) throw new UnknownHostException("host == null");
       return InetAddress.getAllByName(host);
     }
   };
diff --git a/okhttp/src/test/java/com/squareup/okhttp/internal/http/URLConnectionTest.java b/okhttp/src/test/java/com/squareup/okhttp/internal/http/URLConnectionTest.java
index 05fd46973..36312ed37 100644
--- a/okhttp/src/test/java/com/squareup/okhttp/internal/http/URLConnectionTest.java
+++ b/okhttp/src/test/java/com/squareup/okhttp/internal/http/URLConnectionTest.java
@@ -399,6 +399,17 @@ public final class URLConnectionTest {
     testServerClosesOutput(SHUTDOWN_OUTPUT_AT_END);
   }
 
+  @Test public void invalidHost() throws Exception {
+    // Note that 1234.1.1.1 is an invalid host in a URI, but URL isn't as strict.
+    URL url = new URL("http://1234.1.1.1/index.html");
+    HttpURLConnection connection = client.open(url);
+    try {
+      connection.connect();
+      fail();
+    } catch (UnknownHostException expected) {
+    }
+  }
+
   private void testServerClosesOutput(SocketPolicy socketPolicy) throws Exception {
     server.enqueue(new MockResponse().setBody("This connection won't pool properly")
         .setSocketPolicy(socketPolicy));