diff --git a/.gitignore b/.gitignore
index fb6c963..b93909d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 .php_cs.cache
 build
+coverage
 composer.lock
 phpunit.xml
 vendor
diff --git a/lib/ResourceOutputStream.php b/lib/ResourceOutputStream.php
index dab9dd1..5bb2d90 100644
--- a/lib/ResourceOutputStream.php
+++ b/lib/ResourceOutputStream.php
@@ -28,7 +28,10 @@ class ResourceOutputStream implements OutputStream {
 
         $meta = \stream_get_meta_data($stream);
 
-        if (isset($meta["mode"]) && $meta["mode"] === "r") {
+        if (isset($meta["mode"])
+            && \strpos($meta["mode"], "r") !== false
+            && \strpos($meta["mode"], "+") === false
+        ) {
             throw new \Error("Expected a writable stream");
         }
 
diff --git a/test/MessageTest.php b/test/MessageTest.php
index 04de2df..6aa650e 100644
--- a/test/MessageTest.php
+++ b/test/MessageTest.php
@@ -2,8 +2,10 @@
 
 namespace Amp\ByteStream\Test;
 
+use Amp\ByteStream\InMemoryStream;
 use Amp\ByteStream\IteratorStream;
 use Amp\ByteStream\Message;
+use Amp\ByteStream\PendingReadError;
 use Amp\Emitter;
 use Amp\Loop;
 use Amp\PHPUnit\TestCase;
@@ -159,4 +161,39 @@ class MessageTest extends TestCase {
             $this->assertNull(yield $stream->read());
         });
     }
+
+    public function testGetInputStream() {
+        Loop::run(function () {
+            $inputStream = new InMemoryStream("");
+            $message = new Message($inputStream);
+
+            $this->assertSame($inputStream, $message->getInputStream());
+            $this->assertSame("", yield $message->getInputStream()->read());
+        });
+    }
+
+    public function testPendingRead() {
+        Loop::run(function () {
+            $emitter = new Emitter;
+            $stream = new Message(new IteratorStream($emitter->iterate()));
+
+            Loop::delay(0, function () use ($emitter) {
+                $emitter->emit("test");
+            });
+
+            $this->assertSame("test", yield $stream->read());
+        });
+    }
+
+    public function testPendingReadError() {
+        Loop::run(function () {
+            $emitter = new Emitter;
+            $stream = new Message(new IteratorStream($emitter->iterate()));
+            $stream->read();
+
+            $this->expectException(PendingReadError::class);
+
+            $stream->read();
+        });
+    }
 }
diff --git a/test/ResourceInputStreamTest.php b/test/ResourceInputStreamTest.php
new file mode 100644
index 0000000..9f3ab2e
--- /dev/null
+++ b/test/ResourceInputStreamTest.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace Amp\ByteStream\Test;
+
+use Amp\ByteStream\ResourceInputStream;
+use PHPUnit\Framework\TestCase;
+
+class ResourceInputStreamTest extends TestCase {
+    public function testGetResource() {
+        $stream = new ResourceInputStream(\STDIN);
+
+        $this->assertSame(\STDIN, $stream->getResource());
+    }
+
+    public function testNonStream() {
+        $this->expectException(\Error::class);
+        $this->expectExceptionMessage("Expected a valid stream");
+
+        new ResourceInputStream(42);
+    }
+
+    public function testNotReadable() {
+        $this->expectException(\Error::class);
+        $this->expectExceptionMessage("Expected a readable stream");
+
+        new ResourceInputStream(\STDOUT);
+    }
+}
diff --git a/test/ResourceOutputStreamTest.php b/test/ResourceOutputStreamTest.php
new file mode 100644
index 0000000..3949fe5
--- /dev/null
+++ b/test/ResourceOutputStreamTest.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace Amp\ByteStream\Test;
+
+use Amp\ByteStream\ResourceOutputStream;
+use PHPUnit\Framework\TestCase;
+
+class ResourceOutputStreamTest extends TestCase {
+    public function testGetResource() {
+        $stream = new ResourceOutputStream(\STDOUT);
+
+        $this->assertSame(\STDOUT, $stream->getResource());
+    }
+
+    public function testNonStream() {
+        $this->expectException(\Error::class);
+        $this->expectExceptionMessage("Expected a valid stream");
+
+        new ResourceOutputStream(42);
+    }
+
+    public function testNotWritable() {
+        $this->expectException(\Error::class);
+        $this->expectExceptionMessage("Expected a writable stream");
+
+        new ResourceOutputStream(\STDIN);
+    }
+}