diff --git a/functionMap.php b/functionMap.php
index eabe428..ced5882 100644
--- a/functionMap.php
+++ b/functionMap.php
@@ -130,7 +130,7 @@
     'register_post_type' => [null, 'post_type' => 'lowercase-string&non-empty-string'],
     'render_block_core_categories' => ['non-falsy-string'],
     'rest_authorization_required_code' => ['401|403'],
-    'rest_sanitize_boolean' => ["(T is bool ? T : (T is ''|'false'|'FALSE'|'0'|0 ? false : true))", '@phpstan-template T' => 'of bool|string|int', 'value' => 'T'],
+    'rest_sanitize_boolean' => ["(T is bool ? T : (T is ''|'false'|'FALSE'|'0'|0 ? false : true))", '@phpstan-template T' => 'of bool|string|int', 'value' => 'T', '@phpstan-pure' => ''],
     'rest_ensure_response' => ['($response is \WP_Error ? \WP_Error : \WP_REST_Response)'],
     'sanitize_bookmark_field' => ['array<int, int>|int|string', 'field' => "'link_id'|'link_url'|'link_name'|'link_image'|'link_target'|'link_description'|'link_visible'|'link_owner'|'link_rating'|'link_updated'|'link_rel'|'link_notes'|'link_rss'|'link_category'"],
     'sanitize_category' => ['T', '@phpstan-template' => 'T of array|object', 'category' => 'T'],
diff --git a/tests/data/pure/rest-sanitize-boolean.php b/tests/data/pure/rest-sanitize-boolean.php
new file mode 100644
index 0000000..947a591
--- /dev/null
+++ b/tests/data/pure/rest-sanitize-boolean.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpStubs\WordPress\Core\Tests;
+
+use function rest_sanitize_boolean;
+use function PHPStan\Testing\assertType;
+
+$toSanitize = Faker::mixed();
+
+assertType('bool', rest_sanitize_boolean($toSanitize));
+
+if (rest_sanitize_boolean($toSanitize)) {
+    assertType('true', rest_sanitize_boolean($toSanitize));
+}
+
+if (! rest_sanitize_boolean($toSanitize)) {
+    assertType('false', rest_sanitize_boolean($toSanitize));
+}
diff --git a/wordpress-stubs.php b/wordpress-stubs.php
index b57b29d..a89826b 100644
--- a/wordpress-stubs.php
+++ b/wordpress-stubs.php
@@ -135481,6 +135481,7 @@ function rest_is_ip_address($ip)
      * @return bool Returns the proper associated boolean value.
      * @phpstan-template T of bool|string|int
      * @phpstan-param T $value
+     * @phpstan-pure
      * @phpstan-return (T is bool ? T : (T is ''|'false'|'FALSE'|'0'|0 ? false : true))
      */
     function rest_sanitize_boolean($value)