diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index 9baee0ab6b3fd..2e7bf089c1623 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -44,7 +44,6 @@ includes:
 	- tests/phpstan/baselines/method.childParameterType.neon
 	- tests/phpstan/baselines/method.unused.neon
 	- tests/phpstan/baselines/notIdentical.alwaysTrue.neon
-	- tests/phpstan/baselines/nullCoalesce.property.neon
 	- tests/phpstan/baselines/offsetAccess.nonOffsetAccessible.neon
 	- tests/phpstan/baselines/offsetAccess.notFound.neon
 	- tests/phpstan/baselines/offsetAssign.valueType.neon
diff --git a/src/wp-includes/class-wp-query.php b/src/wp-includes/class-wp-query.php
index 88981421ff937..2b593c0addd6b 100644
--- a/src/wp-includes/class-wp-query.php
+++ b/src/wp-includes/class-wp-query.php
@@ -186,6 +186,7 @@ class WP_Query {
 	 *
 	 * @since 2.1.0
 	 * @var int
+	 * @phpstan-var int<0, max>
 	 */
 	public $max_num_pages = 0;
 
@@ -3732,7 +3733,7 @@ private function set_found_posts( $query_vars, $limits ) {
 		$this->found_posts = (int) apply_filters_ref_array( 'found_posts', array( $this->found_posts, &$this ) );
 
 		if ( ! empty( $limits ) ) {
-			$this->max_num_pages = (int) ceil( $this->found_posts / $query_vars['posts_per_page'] );
+			$this->max_num_pages = max( 0, (int) ceil( $this->found_posts / (int) $query_vars['posts_per_page'] ) );
 		}
 	}
 
diff --git a/src/wp-includes/general-template.php b/src/wp-includes/general-template.php
index eb6e185f5b49d..f91680a9ef44c 100644
--- a/src/wp-includes/general-template.php
+++ b/src/wp-includes/general-template.php
@@ -4983,7 +4983,7 @@ function paginate_links( $args = '' ) {
 	$url_parts    = explode( '?', $pagenum_link );
 
 	// Get max pages and current page out of the current query, if available.
-	$total   = $wp_query->max_num_pages ?? 1;
+	$total   = $wp_query->max_num_pages;
 	$current = get_query_var( 'paged' ) ? (int) get_query_var( 'paged' ) : 1;
 
 	/*
diff --git a/src/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php b/src/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
index c96b12c7e25f6..c1545c26b9105 100644
--- a/src/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
+++ b/src/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
@@ -209,7 +209,7 @@ public function get_max_num_pages( $object_subtype = '' ) {
 		$query = new WP_Query( $args );
 
 		$min_num_pages = ( 'page' === $post_type && 'posts' === get_option( 'show_on_front' ) ) ? 1 : 0;
-		return isset( $query->max_num_pages ) ? max( $min_num_pages, $query->max_num_pages ) : 1;
+		return max( $min_num_pages, $query->max_num_pages );
 	}
 
 	/**
diff --git a/tests/phpstan/baselines/isset.property.neon b/tests/phpstan/baselines/isset.property.neon
index 063b443d92227..5278005df2869 100644
--- a/tests/phpstan/baselines/isset.property.neon
+++ b/tests/phpstan/baselines/isset.property.neon
@@ -178,11 +178,6 @@ parameters:
 			identifier: isset.property
 			count: 1
 			path: ../../../src/wp-includes/rest-api/endpoints/class-wp-rest-font-families-controller.php
-		-
-			message: '#^Property WP_Query\:\:\$max_num_pages \(int\) in isset\(\) is not nullable\.$#'
-			identifier: isset.property
-			count: 1
-			path: ../../../src/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
 		-
 			message: '#^Property WP_Site\:\:\$domain \(string\) in isset\(\) is not nullable\.$#'
 			identifier: isset.property
diff --git a/tests/phpstan/baselines/nullCoalesce.property.neon b/tests/phpstan/baselines/nullCoalesce.property.neon
deleted file mode 100644
index 0085e07d9614f..0000000000000
--- a/tests/phpstan/baselines/nullCoalesce.property.neon
+++ /dev/null
@@ -1,25 +0,0 @@
-# PHPStan baseline for the `nullCoalesce.property` errors in WordPress core.
-#
-# https://phpstan.org/error-identifiers/nullCoalesce.property
-#
-# Each entry is scoped to a single file and carries an exact occurrence count,
-# so that a new instance is reported as a new error rather than being absorbed
-# silently. Fixing an occurrence therefore means decrementing or removing its
-# entry here as part of the same change.
-#
-# The goal is to empty this file and delete it, along with the `includes` entry
-# for it in phpstan.neon.dist.
-#
-# Generated by `composer phpstan:baselines`. Do not edit by hand; regenerate with
-#
-#     composer phpstan:baselines -- --identifier=nullCoalesce.property
-#
-# which reruns the analysis with this file suppressed so the errors surface again.
-
-parameters:
-	ignoreErrors:
-		-
-			message: '#^Property WP_Query\:\:\$max_num_pages \(int\) on left side of \?\? is not nullable\.$#'
-			identifier: nullCoalesce.property
-			count: 1
-			path: ../../../src/wp-includes/general-template.php
diff --git a/tests/phpunit/tests/query/noFoundRows.php b/tests/phpunit/tests/query/noFoundRows.php
index 7b4f66a416030..e9ffcd6581362 100644
--- a/tests/phpunit/tests/query/noFoundRows.php
+++ b/tests/phpunit/tests/query/noFoundRows.php
@@ -102,4 +102,62 @@ public function test_no_found_rows_default_with_postsperpage_minus1() {
 		$this->assertStringNotContainsString( 'SQL_CALC_FOUND_ROWS', $q->request );
 		$this->assertSame( 1, $q->found_posts );
 	}
+
+	/**
+	 * Ensures {@see WP_Query::$max_num_pages} is not negative when the
+	 * {@see 'found_posts'} filter returns a negative count.
+	 *
+	 * @ticket 65817
+	 */
+	public function test_max_num_pages_is_not_negative_when_found_posts_is_filtered_negative() {
+		self::factory()->post->create_many( 3 );
+
+		add_filter(
+			'found_posts',
+			static function (): int {
+				return -5;
+			}
+		);
+
+		$q = new WP_Query(
+			array(
+				'post_type'      => 'post',
+				'posts_per_page' => 2,
+			)
+		);
+
+		$this->assertSame( -5, $q->found_posts, 'Expected the filtered found_posts value to be kept.' );
+		$this->assertSame( 0, $q->max_num_pages, 'Expected max_num_pages to be clamped to zero.' );
+	}
+
+	/**
+	 * Ensures {@see WP_Query::$max_num_pages} is not negative when a
+	 * {@see 'post_limits'} filter injects a non-empty `LIMIT` clause on a
+	 * `posts_per_page = -1` query, which otherwise never runs the found-rows
+	 * calculation and skips the `max_num_pages` division entirely.
+	 *
+	 * @ticket 65817
+	 */
+	public function test_max_num_pages_is_not_negative_when_limits_are_filtered_with_postsperpage_minus1() {
+		self::factory()->post->create_many( 3 );
+
+		add_filter(
+			'post_limits',
+			static function (): string {
+				return 'LIMIT 0, 2';
+			}
+		);
+
+		$q = new WP_Query(
+			array(
+				'post_type'      => 'post',
+				'posts_per_page' => -1,
+			)
+		);
+
+		$this->assertIsString( $q->request );
+		$this->assertStringContainsString( 'SQL_CALC_FOUND_ROWS', $q->request, 'Expected the filtered LIMIT to trigger the found-rows query.' );
+		$this->assertSame( 3, $q->found_posts, 'Expected found_posts to reflect all matching rows.' );
+		$this->assertSame( 0, $q->max_num_pages, 'Expected max_num_pages to be clamped to zero.' );
+	}
 }