diff --git a/lib/UvHandle.php b/lib/UvHandle.php
index d693a76..1095e3f 100644
--- a/lib/UvHandle.php
+++ b/lib/UvHandle.php
@@ -176,10 +176,10 @@ class UvHandle implements Handle
                 }
             } else {
                 StatCache::clear($this->path);
-                $newPosition = $this->position + $length;
-                $delta = $newPosition - $this->position;
-                $this->position = ($this->mode[0] === "a") ? $this->position : $newPosition;
-                $this->size += $delta;
+                $this->position += $length;
+                if ($this->position > $this->size) {
+                    $this->size = $this->position;
+                }
                 $deferred->resolve($length);
             }
         };
diff --git a/test/HandleTest.php b/test/HandleTest.php
index 8aedf87..13cea7d 100644
--- a/test/HandleTest.php
+++ b/test/HandleTest.php
@@ -94,6 +94,23 @@ abstract class HandleTest extends TestCase
         });
     }
 
+    public function testWriteInAppendMode()
+    {
+        $this->execute(function () {
+            $path = Fixture::path() . "/write";
+            /** @var \Amp\File\Handle $handle */
+            $handle = yield File\open($path, "a+");
+            $this->assertSame(0, $handle->tell());
+            yield $handle->write("bar");
+            yield $handle->write("foo");
+            yield $handle->write("baz");
+            $this->assertSame(9, $handle->tell());
+            yield $handle->seek(0);
+            $this->assertSame(0, $handle->tell());
+            $this->assertSame("barfoobaz", yield $handle->read());
+        });
+    }
+
     public function testReadingToEof()
     {
         $this->execute(function () {