diff --git a/composer.json b/composer.json
index 9660ee9..7166595 100644
--- a/composer.json
+++ b/composer.json
@@ -17,8 +17,7 @@
         "psr/http-client-implementation": "^1",
         "psr/http-factory": "^1.0",
         "psr/http-factory-implementation": "^1",
-        "psr/http-message": "^1.0 || ^2.0",
-        "webmozart/assert": "^1.11"
+        "psr/http-message": "^1.0 || ^2.0"
     },
     "require-dev": {
         "ergebnis/composer-normalize": "^2.52",
@@ -29,7 +28,6 @@
         "phpstan/phpstan": "^2.2",
         "phpstan/phpstan-phpunit": "^2.0",
         "phpstan/phpstan-strict-rules": "^2.0",
-        "phpstan/phpstan-webmozart-assert": "^2.0",
         "phpunit/phpunit": "^10.5",
         "rector/rector": "^2.0",
         "shipmonk/composer-dependency-analyser": "^1.8",
diff --git a/src/Request/CollectionRequestOptions.php b/src/Request/CollectionRequestOptions.php
index 4184532..ea4512e 100644
--- a/src/Request/CollectionRequestOptions.php
+++ b/src/Request/CollectionRequestOptions.php
@@ -4,8 +4,6 @@
 
 namespace Setono\Quickpay\Request;
 
-use Webmozart\Assert\Assert;
-
 /**
  * Immutable options for a paginated list request: which page and how many entries per page.
  *
@@ -19,13 +17,13 @@ public function __construct(
         public readonly int $page = 1,
         public readonly int $pageSize = 20,
     ) {
-        Assert::greaterThanEq($page, 1);
-        Assert::greaterThanEq($pageSize, 1);
-    }
+        if ($page < 1) {
+            throw new \InvalidArgumentException(sprintf('Expected $page to be at least 1, got %d.', $page));
+        }
 
-    public static function new(): self
-    {
-        return new self();
+        if ($pageSize < 1) {
+            throw new \InvalidArgumentException(sprintf('Expected $pageSize to be at least 1, got %d.', $pageSize));
+        }
     }
 
     public function withPage(int $page): self
diff --git a/tests/Request/CollectionRequestOptionsTest.php b/tests/Request/CollectionRequestOptionsTest.php
index 966e6f4..eb26cb2 100644
--- a/tests/Request/CollectionRequestOptionsTest.php
+++ b/tests/Request/CollectionRequestOptionsTest.php
@@ -42,7 +42,7 @@ public function it_maps_to_the_page_and_page_size_query_params(): void
     #[Test]
     public function it_builds_modified_copies_immutably(): void
     {
-        $opts = CollectionRequestOptions::new();
+        $opts = new CollectionRequestOptions();
 
         self::assertSame(1, $opts->page);
         self::assertSame(20, $opts->pageSize);