diff --git a/okhttp-tests/src/test/java/com/squareup/okhttp/CallTest.java b/okhttp-tests/src/test/java/com/squareup/okhttp/CallTest.java
index cefb681be..0f0852f4d 100644
--- a/okhttp-tests/src/test/java/com/squareup/okhttp/CallTest.java
+++ b/okhttp-tests/src/test/java/com/squareup/okhttp/CallTest.java
@@ -1393,8 +1393,7 @@ public final class CallTest {
         .matches("okhttp/\\d\\.\\d\\.\\d(-SNAPSHOT)?"));
   }
 
-  @Test
-  public void setFollowRedirectsFalse() throws Exception {
+  @Test public void setFollowRedirectsFalse() throws Exception {
     server.enqueue(new MockResponse()
         .setResponseCode(302)
         .addHeader("Location: /b")
diff --git a/okhttp-tests/src/test/java/com/squareup/okhttp/OkHttpClientTest.java b/okhttp-tests/src/test/java/com/squareup/okhttp/OkHttpClientTest.java
index 7ecd2a1ff..41cdcf43e 100644
--- a/okhttp-tests/src/test/java/com/squareup/okhttp/OkHttpClientTest.java
+++ b/okhttp-tests/src/test/java/com/squareup/okhttp/OkHttpClientTest.java
@@ -35,6 +35,7 @@ import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 public final class OkHttpClientTest {
   private static final ProxySelector DEFAULT_PROXY_SELECTOR = ProxySelector.getDefault();
@@ -164,4 +165,13 @@ public final class OkHttpClientTest {
     Response actualResponse = mockClient.newCall(request).execute();
     assertSame(response, actualResponse);
   }
+
+  @Test public void setProtocolsRejectsHttp10() throws Exception {
+    OkHttpClient client = new OkHttpClient();
+    try {
+      client.setProtocols(Arrays.asList(Protocol.HTTP_1_0, Protocol.HTTP_1_1));
+      fail();
+    } catch (IllegalArgumentException expected) {
+    }
+  }
 }
diff --git a/okhttp/src/main/java/com/squareup/okhttp/OkHttpClient.java b/okhttp/src/main/java/com/squareup/okhttp/OkHttpClient.java
index 69029dfa4..d99a961cc 100644
--- a/okhttp/src/main/java/com/squareup/okhttp/OkHttpClient.java
+++ b/okhttp/src/main/java/com/squareup/okhttp/OkHttpClient.java
@@ -427,14 +427,22 @@ public class OkHttpClient implements Cloneable {
    * <a href="http://tools.ietf.org/html/draft-ietf-tls-applayerprotoneg">ALPN</a>
    * will be used to negotiate a transport.
    *
+   * <p>{@link Protocol#HTTP_1_0} is not supported in this set. Requests are
+   * initiated with {@code HTTP/1.1} only. If the server responds with {@code
+   * HTTP/1.0}, that will be exposed by {@link Response#protocol()}.
+   *
    * @param protocols the protocols to use, in order of preference. The list
-   *     must contain {@link Protocol#HTTP_1_1}. It must not contain null.
+   *     must contain {@link Protocol#HTTP_1_1}. It must not contain null or
+   *     {@link Protocol#HTTP_1_0}.
    */
   public final OkHttpClient setProtocols(List<Protocol> protocols) {
     protocols = Util.immutableList(protocols);
     if (!protocols.contains(Protocol.HTTP_1_1)) {
       throw new IllegalArgumentException("protocols doesn't contain http/1.1: " + protocols);
     }
+    if (protocols.contains(Protocol.HTTP_1_0)) {
+      throw new IllegalArgumentException("protocols must not contain http/1.0: " + protocols);
+    }
     if (protocols.contains(null)) {
       throw new IllegalArgumentException("protocols must not contain null");
     }