diff --git a/lib/Loop.php b/lib/Loop.php
index 800000b..eb42631 100644
--- a/lib/Loop.php
+++ b/lib/Loop.php
@@ -81,7 +81,7 @@ final class Loop {
      * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      */
     public static function defer(callable $callback, $data = null): string {
-        return self::$driver->defer(wrap($callback), $data);
+        return self::$driver->defer($callback, $data);
     }
 
     /**
@@ -101,7 +101,7 @@ final class Loop {
      * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      */
     public static function delay(int $delay, callable $callback, $data = null): string {
-        return self::$driver->delay($delay, wrap($callback), $data);
+        return self::$driver->delay($delay, $callback, $data);
     }
 
     /**
@@ -121,7 +121,7 @@ final class Loop {
      * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      */
     public static function repeat(int $interval, callable $callback, $data = null): string {
-        return self::$driver->repeat($interval, wrap($callback), $data);
+        return self::$driver->repeat($interval, $callback, $data);
     }
 
     /**
@@ -144,7 +144,7 @@ final class Loop {
      * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      */
     public static function onReadable($stream, callable $callback, $data = null): string {
-        return self::$driver->onReadable($stream, wrap($callback), $data);
+        return self::$driver->onReadable($stream, $callback, $data);
     }
 
     /**
@@ -167,7 +167,7 @@ final class Loop {
      * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      */
     public static function onWritable($stream, callable $callback, $data = null): string {
-        return self::$driver->onWritable($stream, wrap($callback), $data);
+        return self::$driver->onWritable($stream, $callback, $data);
     }
 
     /**
@@ -191,7 +191,7 @@ final class Loop {
      * @throws UnsupportedFeatureException If signal handling is not supported.
      */
     public static function onSignal(int $signo, callable $callback, $data = null): string {
-        return self::$driver->onSignal($signo, wrap($callback), $data);
+        return self::$driver->onSignal($signo, $callback, $data);
     }
 
     /**
diff --git a/lib/Loop/Driver.php b/lib/Loop/Driver.php
index 2c7d4e0..1ec9aa7 100644
--- a/lib/Loop/Driver.php
+++ b/lib/Loop/Driver.php
@@ -2,7 +2,10 @@
 
 namespace Amp\Loop;
 
+use Amp\Coroutine;
+use Amp\Promise;
 use Amp\Internal\Watcher;
+use function Amp\rethrow;
 
 /**
  * Event loop driver which implements all basic operations to allow interoperability.
@@ -104,7 +107,15 @@ abstract class Driver {
                 unset($this->watchers[$watcher->id], $this->deferQueue[$watcher->id]);
 
                 $callback = $watcher->callback;
-                $callback($watcher->id, $watcher->data);
+                $result = $callback($watcher->id, $watcher->data);
+
+                if ($result instanceof \Generator) {
+                    $result = new Coroutine($result);
+                }
+
+                if ($result instanceof Promise) {
+                    rethrow($result);
+                }
             }
 
             $this->dispatch(empty($this->nextTickQueue) && empty($this->enableQueue) && $this->running);
diff --git a/lib/Loop/EvLoop.php b/lib/Loop/EvLoop.php
index 12ebd3b..64a2429 100644
--- a/lib/Loop/EvLoop.php
+++ b/lib/Loop/EvLoop.php
@@ -2,7 +2,10 @@
 
 namespace Amp\Loop;
 
+use Amp\Coroutine;
+use Amp\Promise;
 use Amp\Internal\Watcher;
+use function Amp\rethrow;
 
 class EvLoop extends Driver {
     /** @var \EvSignal[]|null */
@@ -32,7 +35,15 @@ class EvLoop extends Driver {
             $watcher = $event->data;
 
             $callback = $watcher->callback;
-            $callback($watcher->id, $watcher->value, $watcher->data);
+            $result = $callback($watcher->id, $watcher->value, $watcher->data);
+
+            if ($result instanceof \Generator) {
+                $result = new Coroutine($result);
+            }
+
+            if ($result instanceof Promise) {
+                rethrow($result);
+            }
         };
 
         $this->timerCallback = function (\EvTimer $event) {
@@ -44,7 +55,15 @@ class EvLoop extends Driver {
             }
 
             $callback = $watcher->callback;
-            $callback($watcher->id, $watcher->data);
+            $result = $callback($watcher->id, $watcher->data);
+
+            if ($result instanceof \Generator) {
+                $result = new Coroutine($result);
+            }
+
+            if ($result instanceof Promise) {
+                rethrow($result);
+            }
         };
 
         $this->signalCallback = function (\EvSignal $event) {
@@ -52,7 +71,15 @@ class EvLoop extends Driver {
             $watcher = $event->data;
 
             $callback = $watcher->callback;
-            $callback($watcher->id, $watcher->value, $watcher->data);
+            $result = $callback($watcher->id, $watcher->value, $watcher->data);
+
+            if ($result instanceof \Generator) {
+                $result = new Coroutine($result);
+            }
+
+            if ($result instanceof Promise) {
+                rethrow($result);
+            }
         };
     }
 
diff --git a/lib/Loop/EventLoop.php b/lib/Loop/EventLoop.php
index e8850d9..ea180ba 100644
--- a/lib/Loop/EventLoop.php
+++ b/lib/Loop/EventLoop.php
@@ -2,7 +2,10 @@
 
 namespace Amp\Loop;
 
+use Amp\Coroutine;
+use Amp\Promise;
 use Amp\Internal\Watcher;
+use function Amp\rethrow;
 
 class EventLoop extends Driver {
     /** @var \Event[]|null */
@@ -29,7 +32,15 @@ class EventLoop extends Driver {
 
         $this->ioCallback = function ($resource, $what, Watcher $watcher) {
             $callback = $watcher->callback;
-            $callback($watcher->id, $watcher->value, $watcher->data);
+            $result = $callback($watcher->id, $watcher->value, $watcher->data);
+
+            if ($result instanceof \Generator) {
+                $result = new Coroutine($result);
+            }
+
+            if ($result instanceof Promise) {
+                rethrow($result);
+            }
         };
 
         $this->timerCallback = function ($resource, $what, Watcher $watcher) {
@@ -38,12 +49,28 @@ class EventLoop extends Driver {
             }
 
             $callback = $watcher->callback;
-            $callback($watcher->id, $watcher->data);
+            $result = $callback($watcher->id, $watcher->data);
+
+            if ($result instanceof \Generator) {
+                $result = new Coroutine($result);
+            }
+
+            if ($result instanceof Promise) {
+                rethrow($result);
+            }
         };
 
         $this->signalCallback = function ($signum, $what, Watcher $watcher) {
             $callback = $watcher->callback;
-            $callback($watcher->id, $watcher->value, $watcher->data);
+            $result = $callback($watcher->id, $watcher->value, $watcher->data);
+
+            if ($result instanceof \Generator) {
+                $result = new Coroutine($result);
+            }
+
+            if ($result instanceof Promise) {
+                rethrow($result);
+            }
         };
     }
 
diff --git a/lib/Loop/NativeLoop.php b/lib/Loop/NativeLoop.php
index 3226926..b6ab4bd 100644
--- a/lib/Loop/NativeLoop.php
+++ b/lib/Loop/NativeLoop.php
@@ -2,7 +2,10 @@
 
 namespace Amp\Loop;
 
+use Amp\Coroutine;
+use Amp\Promise;
 use Amp\Internal\Watcher;
+use function Amp\rethrow;
 
 class NativeLoop extends Driver {
     /** @var resource[] */
@@ -89,7 +92,15 @@ class NativeLoop extends Driver {
 
                 // Execute the timer.
                 $callback = $watcher->callback;
-                $callback($id, $watcher->data);
+                $result = $callback($id, $watcher->data);
+
+                if ($result instanceof \Generator) {
+                    $result = new Coroutine($result);
+                }
+
+                if ($result instanceof Promise) {
+                    rethrow($result);
+                }
             }
         }
 
@@ -130,7 +141,15 @@ class NativeLoop extends Driver {
                             }
 
                             $callback = $watcher->callback;
-                            $callback($watcher->id, $stream, $watcher->data);
+                            $result = $callback($watcher->id, $stream, $watcher->data);
+
+                            if ($result instanceof \Generator) {
+                                $result = new Coroutine($result);
+                            }
+
+                            if ($result instanceof Promise) {
+                                rethrow($result);
+                            }
                         }
                     }
                 }
@@ -144,7 +163,15 @@ class NativeLoop extends Driver {
                             }
 
                             $callback = $watcher->callback;
-                            $callback($watcher->id, $stream, $watcher->data);
+                            $result = $callback($watcher->id, $stream, $watcher->data);
+
+                            if ($result instanceof \Generator) {
+                                $result = new Coroutine($result);
+                            }
+
+                            if ($result instanceof Promise) {
+                                rethrow($result);
+                            }
                         }
                     }
                 }
@@ -277,7 +304,15 @@ class NativeLoop extends Driver {
             }
 
             $callback = $watcher->callback;
-            $callback($watcher->id, $signo, $watcher->data);
+            $result = $callback($watcher->id, $signo, $watcher->data);
+
+            if ($result instanceof \Generator) {
+                $result = new Coroutine($result);
+            }
+
+            if ($result instanceof Promise) {
+                rethrow($result);
+            }
         }
     }
 }
diff --git a/lib/Loop/UvLoop.php b/lib/Loop/UvLoop.php
index 88b7455..bac7318 100644
--- a/lib/Loop/UvLoop.php
+++ b/lib/Loop/UvLoop.php
@@ -2,7 +2,10 @@
 
 namespace Amp\Loop;
 
+use Amp\Coroutine;
+use Amp\Promise;
 use Amp\Internal\Watcher;
+use function Amp\rethrow;
 
 class UvLoop extends Driver {
     /** @var resource A uv_loop resource created with uv_loop_new() */
@@ -54,7 +57,15 @@ class UvLoop extends Driver {
 
             foreach ($watchers as $watcher) {
                 $callback = $watcher->callback;
-                $callback($watcher->id, $resource, $watcher->data);
+                $result = $callback($watcher->id, $resource, $watcher->data);
+
+                if ($result instanceof \Generator) {
+                    $result = new Coroutine($result);
+                }
+
+                if ($result instanceof Promise) {
+                    rethrow($result);
+                }
             }
         };
 
@@ -66,14 +77,30 @@ class UvLoop extends Driver {
             }
 
             $callback = $watcher->callback;
-            $callback($watcher->id, $watcher->data);
+            $result = $callback($watcher->id, $watcher->data);
+
+            if ($result instanceof \Generator) {
+                $result = new Coroutine($result);
+            }
+
+            if ($result instanceof Promise) {
+                rethrow($result);
+            }
         };
 
         $this->signalCallback = function ($event, $signo) {
             $watcher = $this->watchers[(int) $event];
 
             $callback = $watcher->callback;
-            $callback($watcher->id, $signo, $watcher->data);
+            $result = $callback($watcher->id, $signo, $watcher->data);
+
+            if ($result instanceof \Generator) {
+                $result = new Coroutine($result);
+            }
+
+            if ($result instanceof Promise) {
+                rethrow($result);
+            }
         };
     }