diff --git a/lib/Internal/Producer.php b/lib/Internal/Producer.php
index ad6a786..33751a3 100644
--- a/lib/Internal/Producer.php
+++ b/lib/Internal/Producer.php
@@ -15,6 +15,7 @@ use React\Promise\PromiseInterface as ReactPromise;
  * before emitting values.
  *
  * @internal
+ * @template-covariant TValue
  */
 trait Producer
 {
@@ -41,6 +42,8 @@ trait Producer
 
     /**
      * {@inheritdoc}
+     *
+     * @return Promise<bool>
      */
     public function advance(): Promise
     {
@@ -72,6 +75,8 @@ trait Producer
 
     /**
      * {@inheritdoc}
+     *
+     * @return Promise<TValue>
      */
     public function getCurrent()
     {
diff --git a/lib/Producer.php b/lib/Producer.php
index 828f2c8..82895f6 100644
--- a/lib/Producer.php
+++ b/lib/Producer.php
@@ -2,12 +2,19 @@
 
 namespace Amp;
 
+/**
+ * @template-covariant TValue
+ * @template-implements Iterator<TValue>
+ */
 final class Producer implements Iterator
 {
+    /**
+     * @use Internal\Producer<TValue>
+     */
     use CallableMaker, Internal\Producer;
 
     /**
-     * @param callable(callable(mixed $value): Promise $emit): \Generator $producer
+     * @param callable(callable(TValue $value): Promise $emit): \Generator $producer
      *
      * @throws \Error Thrown if the callable does not return a Generator.
      */
diff --git a/psalm.xml b/psalm.xml
index 4605917..fe548ca 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -1,7 +1,7 @@
 <?xml version="1.0"?>
 <psalm
         totallyTyped="false"
-        errorLevel="6"
+        errorLevel="5"
         phpVersion="7.0"
         resolveFromConfigFile="true"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"