diff --git a/composer.json b/composer.json
index d7b8699..1af6466 100644
--- a/composer.json
+++ b/composer.json
@@ -37,7 +37,7 @@
         "amphp/phpunit-util": "^3",
         "phpunit/phpunit": "^9",
         "amphp/php-cs-fixer-config": "^2",
-        "psalm/phar": "^5.4"
+        "psalm/phar": "5.22.1"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/Payload.php b/src/Payload.php
index a1755ae..04c04ba 100644
--- a/src/Payload.php
+++ b/src/Payload.php
@@ -130,7 +130,7 @@ public function onClose(\Closure $onClose): void
     }
 
     /**
-     * Buffers entire stream before returning. Use {@see self::buffer()} to optionally provide a{@see Cancellation}
+     * Buffers entire stream before returning. Use {@see self::buffer()} to optionally provide a {@see Cancellation}
      * and/or length limit.
      *
      * @throws BufferException|StreamException
diff --git a/src/ReadableResourceStream.php b/src/ReadableResourceStream.php
index cfeb5c6..644c4b9 100644
--- a/src/ReadableResourceStream.php
+++ b/src/ReadableResourceStream.php
@@ -101,6 +101,8 @@ public function __construct($stream, int $chunkSize = self::DEFAULT_CHUNK_SIZE)
             $useSingleRead,
             $onClose,
         ): void {
+            \assert($stream !== null, 'Watcher invoked with null stream');
+
             \set_error_handler(self::$errorHandler);
 
             try {
diff --git a/src/WritableResourceStream.php b/src/WritableResourceStream.php
index a881e5b..9fffd3a 100644
--- a/src/WritableResourceStream.php
+++ b/src/WritableResourceStream.php
@@ -28,6 +28,7 @@ final class WritableResourceStream implements WritableStream, ResourceStream
 
     private bool $writable = true;
 
+    /** @var positive-int|null */
     private ?int $chunkSize = null;
 
     /** @var \Closure():bool */
@@ -72,8 +73,8 @@ public function __construct($stream, ?int $chunkSize = null)
         $resource = &$this->resource;
 
         $this->callbackId = EventLoop::disable(EventLoop::onWritable(
-            $stream,
-            static function ($callbackId, $stream) use (
+            $this->resource,
+            static function ($callbackId) use (
                 $writes,
                 &$chunkSize,
                 &$writable,
@@ -98,7 +99,8 @@ static function ($callbackId, $stream) use (
                             continue;
                         }
 
-                        if (!\is_resource($stream)) {
+                        /** @psalm-suppress TypeDoesNotContainType */
+                        if (!\is_resource($resource)) {
                             $writable = false;
                             $suspension?->resume(static fn () => throw new ClosedException("The stream was closed by the peer"));
                             continue;
@@ -119,9 +121,9 @@ static function ($callbackId, $stream) use (
                             // Customer error handler needed since fwrite() emits E_WARNING if the pipe is broken or the buffer is full.
                             // Use conditional, because PHP doesn't like getting null passed
                             if ($chunkSize) {
-                                $written = \fwrite($stream, $data, $chunkSize);
+                                $written = \fwrite($resource, $data, $chunkSize);
                             } else {
-                                $written = \fwrite($stream, $data);
+                                $written = \fwrite($resource, $data);
                             }
                         } finally {
                             \restore_error_handler();
@@ -151,6 +153,7 @@ static function ($callbackId, $stream) use (
                         $firstWrite = false;
                     }
                 } finally {
+                    /** @psalm-suppress RedundantCondition */
                     if (!$writable && \is_resource($resource)) {
                         $meta = \stream_get_meta_data($resource);
                         if (\str_contains($meta["mode"], "+")) {
diff --git a/src/functions.php b/src/functions.php
index 9975424..17cd3f9 100644
--- a/src/functions.php
+++ b/src/functions.php
@@ -12,10 +12,12 @@
     );
 } // @codeCoverageIgnoreEnd
 
+/** @psalm-suppress PossiblyInvalidArgument */
 if (!\defined('STDOUT')) {
     \define('STDOUT', \fopen('php://stdout', 'wb'));
 }
 
+/** @psalm-suppress PossiblyInvalidArgument */
 if (!\defined('STDERR')) {
     \define('STDERR', \fopen('php://stderr', 'wb'));
 }