diff --git a/lib/IteratorStream.php b/lib/IteratorStream.php
new file mode 100644
index 0000000..791e4b2
--- /dev/null
+++ b/lib/IteratorStream.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Amp\ByteStream;
+
+use Amp\Deferred;
+use Amp\Iterator;
+use Amp\Promise;
+
+class IteratorStream implements InputStream {
+    private $iterator;
+
+    public function __construct(Iterator $iterator) {
+        $this->iterator = $iterator;
+    }
+
+    /** @inheritdoc */
+    public function read(): Promise {
+        $deferred = new Deferred;
+
+        $this->iterator->advance()->onResolve(function ($error, $hasNextElement) use ($deferred) {
+            if ($error) {
+                $deferred->fail($error);
+            } elseif ($hasNextElement) {
+                $deferred->resolve($this->iterator->getCurrent());
+            } else {
+                $deferred->resolve(null);
+            }
+        });
+
+        return $deferred->promise();
+    }
+}
diff --git a/lib/Message.php b/lib/Message.php
index 016f340..5175578 100644
--- a/lib/Message.php
+++ b/lib/Message.php
@@ -4,28 +4,30 @@ namespace Amp\ByteStream;
 
 use Amp\Coroutine;
 use Amp\Deferred;
-use Amp\Iterator;
 use Amp\Promise;
 use Amp\Success;
 
 /**
- * Creates a buffered message from an Iterator. The message can be consumed in chunks using the read() API or it may be
- * buffered and accessed in its entirety by waiting for the promise to resolve.
+ * Creates a buffered message from an InputStream. The message can be consumed in chunks using the read() API or it may
+ * be buffered and accessed in its entirety by waiting for the promise to resolve.
  *
  * Buffering Example:
  *
- * $stream = new Message($iterator); // $iterator is an instance of \Amp\Iterator emitting only strings.
+ * $stream = new Message($inputStream);
  * $content = yield $stream;
  *
  * Streaming Example:
  *
- * $stream = new Message($iterator); // $iterator is an instance of \Amp\Iterator emitting only strings.
+ * $stream = new Message($inputStream);
  *
  * while (($chunk = yield $stream->read()) !== null) {
  *     // Immediately use $chunk, reducing memory consumption since the entire message is never buffered.
  * }
  */
 class Message implements InputStream, Promise {
+    /** @var InputStream */
+    private $source;
+
     /** @var string */
     private $buffer = "";
 
@@ -45,15 +47,15 @@ class Message implements InputStream, Promise {
     private $complete = false;
 
     /**
-     * @param \Amp\Iterator $iterator An iterator that only emits strings.
+     * @param InputStream $source An iterator that only emits strings.
      */
-    public function __construct(Iterator $iterator) {
-        $this->coroutine = new Coroutine($this->iterate($iterator));
+    public function __construct(InputStream $source) {
+        $this->source = $source;
     }
 
-    private function iterate(Iterator $iterator): \Generator {
-        while (yield $iterator->advance()) {
-            $buffer = $this->buffer .= $iterator->getCurrent();
+    private function consume(): \Generator {
+        while (($chunk = yield $this->source->read()) !== null) {
+            $buffer = $this->buffer .= $chunk;
 
             if ($buffer === "") {
                 continue; // Do not succeed reads with empty string.
@@ -62,12 +64,12 @@ class Message implements InputStream, Promise {
                 $this->pendingRead = null;
                 $this->buffer = "";
                 $deferred->resolve($buffer);
+                $buffer = ""; // Destroy last emitted chunk to free memory.
             } elseif (!$this->buffering) {
+                $buffer = ""; // Destroy last emitted chunk to free memory.
                 $this->backpressure = new Deferred;
                 yield $this->backpressure->promise();
             }
-
-            $buffer = ""; // Destroy last emitted chunk to free memory.
         }
 
         $this->complete = true;
@@ -87,6 +89,10 @@ class Message implements InputStream, Promise {
             throw new PendingReadError;
         }
 
+        if ($this->coroutine === null) {
+            $this->coroutine = new Coroutine($this->consume());
+        }
+
         if ($this->buffer !== "") {
             $buffer = $this->buffer;
             $this->buffer = "";
@@ -114,6 +120,10 @@ class Message implements InputStream, Promise {
     public function onResolve(callable $onResolved) {
         $this->buffering = true;
 
+        if ($this->coroutine === null) {
+            $this->coroutine = new Coroutine($this->consume());
+        }
+
         if ($this->backpressure) {
             $backpressure = $this->backpressure;
             $this->backpressure = null;
@@ -122,4 +132,16 @@ class Message implements InputStream, Promise {
 
         $this->coroutine->onResolve($onResolved);
     }
+
+    /**
+     * Exposes the source input stream.
+     *
+     * This might be required to resolve a promise with an InputStream, because promises in Amp can't be resolved with
+     * other promises.
+     *
+     * @return InputStream
+     */
+    public function getInputStream(): InputStream {
+        return $this->source;
+    }
 }
diff --git a/test/MessageTest.php b/test/MessageTest.php
index 1366b65..04de2df 100644
--- a/test/MessageTest.php
+++ b/test/MessageTest.php
@@ -2,6 +2,7 @@
 
 namespace Amp\ByteStream\Test;
 
+use Amp\ByteStream\IteratorStream;
 use Amp\ByteStream\Message;
 use Amp\Emitter;
 use Amp\Loop;
@@ -13,7 +14,7 @@ class MessageTest extends TestCase {
             $values = ["abc", "def", "ghi"];
 
             $emitter = new Emitter;
-            $stream = new Message($emitter->iterate());
+            $stream = new Message(new IteratorStream($emitter->iterate()));
 
             foreach ($values as $value) {
                 $emitter->emit($value);
@@ -30,7 +31,7 @@ class MessageTest extends TestCase {
             $values = ["abc", "def", "ghi"];
 
             $emitter = new Emitter;
-            $stream = new Message($emitter->iterate());
+            $stream = new Message(new IteratorStream($emitter->iterate()));
 
             foreach ($values as $value) {
                 $emitter->emit($value);
@@ -55,7 +56,7 @@ class MessageTest extends TestCase {
             $values = ["abc", "def", "ghi"];
 
             $emitter = new Emitter;
-            $stream = new Message($emitter->iterate());
+            $stream = new Message(new IteratorStream($emitter->iterate()));
 
             foreach ($values as $value) {
                 $emitter->emit($value);
@@ -78,7 +79,7 @@ class MessageTest extends TestCase {
             $values = ["abc", "def", "ghi"];
 
             $emitter = new Emitter;
-            $stream = new Message($emitter->iterate());
+            $stream = new Message(new IteratorStream($emitter->iterate()));
 
             foreach ($values as $value) {
                 $emitter->emit($value);
@@ -95,7 +96,7 @@ class MessageTest extends TestCase {
             $values = ["abc", "def", "ghi"];
 
             $emitter = new Emitter;
-            $stream = new Message($emitter->iterate());
+            $stream = new Message(new IteratorStream($emitter->iterate()));
 
             $emitter->emit($values[0]);
 
@@ -119,7 +120,7 @@ class MessageTest extends TestCase {
             $value = "abc";
 
             $emitter = new Emitter;
-            $stream = new Message($emitter->iterate());
+            $stream = new Message(new IteratorStream($emitter->iterate()));
 
             $emitter->emit($value);
             $emitter->fail($exception);
@@ -138,7 +139,7 @@ class MessageTest extends TestCase {
         Loop::run(function () {
             $emitter = new Emitter;
             $emitter->complete();
-            $stream = new Message($emitter->iterate());
+            $stream = new Message(new IteratorStream($emitter->iterate()));
 
             $this->assertNull(yield $stream->read());
         });
@@ -149,7 +150,7 @@ class MessageTest extends TestCase {
             $value = "abc";
 
             $emitter = new Emitter;
-            $stream = new Message($emitter->iterate());
+            $stream = new Message(new IteratorStream($emitter->iterate()));
 
             $emitter->emit($value);
             $emitter->complete();