diff --git a/okhttp-tests/src/test/java/okhttp3/URLConnectionTest.java b/okhttp-tests/src/test/java/okhttp3/URLConnectionTest.java
index 35921a02c..2abdacdf9 100644
--- a/okhttp-tests/src/test/java/okhttp3/URLConnectionTest.java
+++ b/okhttp-tests/src/test/java/okhttp3/URLConnectionTest.java
@@ -85,9 +85,9 @@ import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.concurrent.TimeUnit.NANOSECONDS;
 import static okhttp3.TestUtil.defaultClient;
 import static okhttp3.internal.Util.UTF_8;
-import static okhttp3.internal.huc.OkHttpURLConnection.SELECTED_PROTOCOL;
 import static okhttp3.internal.http.StatusLine.HTTP_PERM_REDIRECT;
 import static okhttp3.internal.http.StatusLine.HTTP_TEMP_REDIRECT;
+import static okhttp3.internal.huc.OkHttpURLConnection.SELECTED_PROTOCOL;
 import static okhttp3.mockwebserver.SocketPolicy.DISCONNECT_AFTER_REQUEST;
 import static okhttp3.mockwebserver.SocketPolicy.DISCONNECT_AT_END;
 import static okhttp3.mockwebserver.SocketPolicy.DISCONNECT_AT_START;
@@ -3503,6 +3503,48 @@ public final class URLConnectionTest {
     }
   }
 
+  /** Confirm that runtime exceptions thrown inside of OkHttp propagate to the caller. */
+  @Test public void unexpectedExceptionSync() throws Exception {
+    urlFactory.setClient(urlFactory.client().newBuilder()
+        .dns(new Dns() {
+          @Override public List<InetAddress> lookup(String hostname) {
+            throw new RuntimeException("boom!");
+          }
+        })
+        .build());
+
+    server.enqueue(new MockResponse());
+
+    HttpURLConnection connection = urlFactory.open(server.url("/").url());
+    try {
+      connection.getResponseCode(); // Use the synchronous implementation.
+      fail();
+    } catch (RuntimeException expected) {
+      assertEquals("boom!", expected.getMessage());
+    }
+  }
+
+  /** Confirm that runtime exceptions thrown inside of OkHttp propagate to the caller. */
+  @Test public void unexpectedExceptionAsync() throws Exception {
+    urlFactory.setClient(urlFactory.client().newBuilder()
+        .dns(new Dns() {
+          @Override public List<InetAddress> lookup(String hostname) {
+            throw new RuntimeException("boom!");
+          }
+        })
+        .build());
+
+    server.enqueue(new MockResponse());
+
+    HttpURLConnection connection = urlFactory.open(server.url("/").url());
+    try {
+      connection.connect(); // Force the async implementation.
+      fail();
+    } catch (RuntimeException expected) {
+      assertEquals("boom!", expected.getMessage());
+    }
+  }
+
   private void testInstanceFollowsRedirects(String spec) throws Exception {
     URL url = new URL(spec);
     HttpURLConnection urlConnection = urlFactory.open(url);
diff --git a/okhttp-urlconnection/src/main/java/okhttp3/internal/huc/OkHttpURLConnection.java b/okhttp-urlconnection/src/main/java/okhttp3/internal/huc/OkHttpURLConnection.java
index 6a2a02a7e..aeaa9ec4b 100644
--- a/okhttp-urlconnection/src/main/java/okhttp3/internal/huc/OkHttpURLConnection.java
+++ b/okhttp-urlconnection/src/main/java/okhttp3/internal/huc/OkHttpURLConnection.java
@@ -100,7 +100,7 @@ public final class OkHttpURLConnection extends HttpURLConnection implements Call
   // These fields are guarded by lock.
   private final Object lock = new Object();
   private Response response;
-  private IOException callFailure;
+  private Throwable callFailure;
   Response networkResponse;
   boolean connectPending = true;
   Proxy proxy;
@@ -129,7 +129,7 @@ public final class OkHttpURLConnection extends HttpURLConnection implements Call
           lock.wait(); // Wait 'til the network interceptor is reached or the call fails.
         }
         if (callFailure != null) {
-          throw callFailure;
+          throw propagate(callFailure);
         }
       } catch (InterruptedException e) {
         throw new InterruptedIOException();
@@ -382,6 +382,7 @@ public final class OkHttpURLConnection extends HttpURLConnection implements Call
 
     OkHttpClient.Builder clientBuilder = client.newBuilder();
     clientBuilder.interceptors().clear();
+    clientBuilder.interceptors().add(UnexpectedException.INTERCEPTOR);
     clientBuilder.networkInterceptors().clear();
     clientBuilder.networkInterceptors().add(networkInterceptor);
 
@@ -408,7 +409,7 @@ public final class OkHttpURLConnection extends HttpURLConnection implements Call
     } else if (networkResponse != null) {
       return networkResponse;
     } else if (callFailure != null) {
-      throw callFailure;
+      throw propagate(callFailure);
     }
 
     Call call = buildCall();
@@ -437,7 +438,7 @@ public final class OkHttpURLConnection extends HttpURLConnection implements Call
     }
 
     synchronized (lock) {
-      if (callFailure != null) throw callFailure;
+      if (callFailure != null) throw propagate(callFailure);
       if (response != null) return response;
     }
 
@@ -573,7 +574,7 @@ public final class OkHttpURLConnection extends HttpURLConnection implements Call
 
   @Override public void onFailure(Call call, IOException e) {
     synchronized (lock) {
-      this.callFailure = e;
+      this.callFailure = (e instanceof UnexpectedException) ? e.getCause() : e;
       lock.notifyAll();
     }
   }
@@ -587,6 +588,32 @@ public final class OkHttpURLConnection extends HttpURLConnection implements Call
     }
   }
 
+  static final class UnexpectedException extends IOException {
+    static final Interceptor INTERCEPTOR = new Interceptor() {
+      @Override public Response intercept(Chain chain) throws IOException {
+        try {
+          return chain.proceed(chain.request());
+        } catch (IOException e) {
+          throw e;
+        } catch (Error | RuntimeException e) {
+          throw new UnexpectedException(e);
+        }
+      }
+    };
+
+    public UnexpectedException(Throwable cause) {
+      super(cause);
+    }
+  }
+
+  /** Throws {@code throwable} as either an IOException, RuntimeException, or Error. */
+  private static IOException propagate(Throwable throwable) throws IOException {
+    if (throwable instanceof IOException) throw (IOException) throwable;
+    if (throwable instanceof Error) throw (Error) throwable;
+    if (throwable instanceof RuntimeException) throw (RuntimeException) throwable;
+    throw new AssertionError();
+  }
+
   /**
    * The HttpURLConnection gives the application control between establishing the connection and
    * transmitting the request body. This interceptor stalls async calls right at this point. The