diff --git a/includes/functions.php b/includes/functions.php
index 6a708d3a..b04a5f30 100644
--- a/includes/functions.php
+++ b/includes/functions.php
@@ -3414,7 +3414,13 @@ function thold_check_threshold(&$thold_data) {
 
 	// don't alert for this host if it's selected for maintenance
 	if (api_plugin_is_enabled('maint') || in_array('maint', $plugins, true)) {
-		include_once($config['base_path'] . '/plugins/maint/functions.php');
+		if (file_exists($config['base_path'] . '/plugins/maint/functions.php')) {
+			require_once($config['base_path'] . '/plugins/maint/functions.php');
+		} else if (file_exists($config['base_path'] . '/plugins/maint/includes/functions.php')) {
+			require_once($config['base_path'] . '/plugins/maint/includes/functions.php');
+		} else {
+			cacti_log('ERROR: cannot include maint functions', false, 'THOLD');
+		}
 	}
 
 	if (api_plugin_is_enabled('maint') && plugin_maint_check_cacti_host($thold_data['host_id'])) {
diff --git a/includes/polling.php b/includes/polling.php
index f6d8c313..51b68988 100644
--- a/includes/polling.php
+++ b/includes/polling.php
@@ -465,7 +465,13 @@ function thold_update_host_status() {
 	include_once($config['library_path'] . '/snmp.php');
 
 	if (api_plugin_is_enabled('maint')) {
-		include_once($config['base_path'] . '/plugins/maint/functions.php');
+		if (file_exists($config['base_path'] . '/plugins/maint/functions.php')) {
+			require_once($config['base_path'] . '/plugins/maint/functions.php');
+		} else if (file_exists($config['base_path'] . '/plugins/maint/includes/functions.php')) {
+			require_once($config['base_path'] . '/plugins/maint/includes/functions.php');
+		} else {
+			cacti_log('ERROR: cannot include maint functions', false, 'THOLD');
+		}
 	}
 
 	$ping_failure_count = read_config_option('ping_failure_count');
diff --git a/tests/Fixtures/cacti-root-maint-includes/plugins/maint/includes/functions.php b/tests/Fixtures/cacti-root-maint-includes/plugins/maint/includes/functions.php
new file mode 100644
index 00000000..28247f69
--- /dev/null
+++ b/tests/Fixtures/cacti-root-maint-includes/plugins/maint/includes/functions.php
@@ -0,0 +1,3 @@
+<?php
+// Empty maint plugin fixture using the includes/ layout: the function it would
+// provide is stubbed, so this file only needs to exist at this path.
diff --git a/tests/Fixtures/cacti-root-maint-includes/plugins/thold/css/modern.css b/tests/Fixtures/cacti-root-maint-includes/plugins/thold/css/modern.css
new file mode 100644
index 00000000..0c1ac1e0
--- /dev/null
+++ b/tests/Fixtures/cacti-root-maint-includes/plugins/thold/css/modern.css
@@ -0,0 +1,2 @@
+/* Fixture stylesheet so thold_page_head()'s file_exists() theme-css branch is
+   reachable under the 'modern' theme returned by the test bootstrap. */
diff --git a/tests/Fixtures/cacti-root-maint-includes/plugins/thold/includes/arrays.php b/tests/Fixtures/cacti-root-maint-includes/plugins/thold/includes/arrays.php
new file mode 100644
index 00000000..814fabc4
--- /dev/null
+++ b/tests/Fixtures/cacti-root-maint-includes/plugins/thold/includes/arrays.php
@@ -0,0 +1,3 @@
+<?php
+// Load the plugin arrays through the same path shape as a Cacti installation.
+require dirname(__DIR__, 6) . '/includes/arrays.php';
diff --git a/tests/Fixtures/cacti-root-no-maint/.gitkeep b/tests/Fixtures/cacti-root-no-maint/.gitkeep
new file mode 100644
index 00000000..b8e4794c
--- /dev/null
+++ b/tests/Fixtures/cacti-root-no-maint/.gitkeep
@@ -0,0 +1,3 @@
+# Cacti root fixture with no maint plugin installed, so neither
+# plugins/maint/functions.php nor plugins/maint/includes/functions.php exists.
+# This drives the "cannot include maint functions" error branch.
diff --git a/tests/Fixtures/cacti-root-no-maint/plugins/thold/css/modern.css b/tests/Fixtures/cacti-root-no-maint/plugins/thold/css/modern.css
new file mode 100644
index 00000000..0c1ac1e0
--- /dev/null
+++ b/tests/Fixtures/cacti-root-no-maint/plugins/thold/css/modern.css
@@ -0,0 +1,2 @@
+/* Fixture stylesheet so thold_page_head()'s file_exists() theme-css branch is
+   reachable under the 'modern' theme returned by the test bootstrap. */
diff --git a/tests/Fixtures/cacti-root-no-maint/plugins/thold/includes/arrays.php b/tests/Fixtures/cacti-root-no-maint/plugins/thold/includes/arrays.php
new file mode 100644
index 00000000..814fabc4
--- /dev/null
+++ b/tests/Fixtures/cacti-root-no-maint/plugins/thold/includes/arrays.php
@@ -0,0 +1,3 @@
+<?php
+// Load the plugin arrays through the same path shape as a Cacti installation.
+require dirname(__DIR__, 6) . '/includes/arrays.php';
diff --git a/tests/Helpers/ThresholdScenario.php b/tests/Helpers/ThresholdScenario.php
index 6d771de3..d99099ad 100644
--- a/tests/Helpers/ThresholdScenario.php
+++ b/tests/Helpers/ThresholdScenario.php
@@ -252,9 +252,13 @@ public function referenceStatistics($average, $max, $min, $last, $dsname = 'traf
 	/**
 	 * Put the device into a maintenance window.
 	 *
+	 * @param string|null $cactiRoot Cacti root fixture to resolve the maint
+	 *   include against; defaults to the layout that ships functions.php at the
+	 *   plugin root.
+	 *
 	 * @return self
 	 */
-	public function inMaintenance() {
+	public function inMaintenance($cactiRoot = null) {
 		// Asked more than once per poll, so a queued value would run out.
 		CactiStubs::willAlwaysReturn('api_plugin_is_enabled', true);
 		CactiStubs::willAlwaysReturn('plugin_maint_check_cacti_host', true);
@@ -264,7 +268,7 @@ public function inMaintenance() {
 		 * base_path at a tracked, repository-contained Cacti root fixture so a
 		 * unit test never writes into the caller's Cacti checkout.
 		 */
-		$GLOBALS['config']['base_path'] = dirname(__DIR__) . '/Fixtures/cacti-root';
+		$GLOBALS['config']['base_path'] = $cactiRoot ?? dirname(__DIR__) . '/Fixtures/cacti-root';
 
 		return $this;
 	}
diff --git a/tests/Unit/MaintIncludeResolutionTest.php b/tests/Unit/MaintIncludeResolutionTest.php
new file mode 100644
index 00000000..f5e1127c
--- /dev/null
+++ b/tests/Unit/MaintIncludeResolutionTest.php
@@ -0,0 +1,143 @@
+<?php
+/*
+ +-------------------------------------------------------------------------+
+ | Copyright (C) 2004-2026 The Cacti Group                                 |
+ |                                                                         |
+ | This program is free software; you can redistribute it and/or           |
+ | modify it under the terms of the GNU General Public License             |
+ | as published by the Free Software Foundation; either version 2          |
+ | of the License, or (at your option) any later version.                  |
+ +-------------------------------------------------------------------------+
+ | Cacti: The Complete RRDtool-based Graphing Solution                     |
+ +-------------------------------------------------------------------------+
+ | http://www.cacti.net/                                                   |
+ +-------------------------------------------------------------------------+
+*/
+
+/**
+ * Both maintenance-aware entry points resolve the maint plugin the same way:
+ * the functions.php that ships at the plugin root, the includes/functions.php
+ * of the newer layout, or an error log when neither is present. These tests
+ * drive all three outcomes for thold_check_threshold() and
+ * thold_update_host_status() so a future change to the lookup is caught.
+ */
+final class MaintIncludeResolutionTest extends TestCase {
+	/**
+	 * @return void
+	 */
+	public static function setUpBeforeClass(): void {
+		self::loadPluginSource('includes/functions.php');
+		self::loadPluginSource('includes/polling.php');
+		self::loadPluginSourceAlways('includes/arrays.php');
+		self::loadPluginConstants();
+	}
+
+	/**
+	 * @param array<string, mixed> $overrides
+	 *
+	 * @return ThresholdScenario
+	 */
+	private function baseline(array $overrides = []) {
+		return ThresholdScenario::threshold($overrides + [
+			'thold_type'        => 1,
+			'bl_type'           => 0,
+			'bl_pct_up'         => 10,
+			'bl_pct_down'       => 10,
+			'bl_ref_time_range' => 3600,
+			'bl_fail_trigger'   => 1,
+		])
+			->alertRecipient('ops@example.org')
+			->referenceStatistics(100, 100, 100, 100);
+	}
+
+	/**
+	 * @param string $name
+	 *
+	 * @return string
+	 */
+	private function fixtureRoot($name) {
+		return dirname(__DIR__) . '/Fixtures/' . $name;
+	}
+
+	/**
+	 * The newer maint layout keeps functions.php under includes/; a device in a
+	 * maintenance window still resolves it and suppresses the notification.
+	 *
+	 * @return void
+	 */
+	public function testCheckThresholdResolvesMaintFromIncludesLayout(): void {
+		$outcome = $this->baseline(['lastread' => 500])
+			->inMaintenance($this->fixtureRoot('cacti-root-maint-includes'))
+			->poll();
+
+		$this->assertSame(0, $outcome->mailCount());
+	}
+
+	/**
+	 * With neither maint layout present the include is skipped and the failure
+	 * is logged rather than fatal.
+	 *
+	 * @return void
+	 */
+	public function testCheckThresholdLogsWhenMaintFunctionsMissing(): void {
+		$this->baseline(['lastread' => 500])
+			->inMaintenance($this->fixtureRoot('cacti-root-no-maint'))
+			->poll();
+
+		$this->assertContains('ERROR: cannot include maint functions', CactiStubs::$log);
+	}
+
+	/**
+	 * Drive thold_update_host_status() far enough to run the maint include
+	 * block. Downstream work needs a live Cacti, so engine messages are
+	 * swallowed and any throw past the block is ignored.
+	 *
+	 * @param string $cactiRoot
+	 *
+	 * @return void
+	 */
+	private function runHostStatus($cactiRoot) {
+		CactiStubs::willAlwaysReturn('api_plugin_is_enabled', true);
+		CactiStubs::$configOptions['alert_deadnotify'] = 'on';
+		$GLOBALS['config']['base_path'] = $cactiRoot;
+
+		set_error_handler(static fn (): bool => true);
+		ob_start();
+
+		try {
+			thold_update_host_status();
+		} catch (\Throwable $e) {
+			// Reaching the maint include block is the point.
+		} finally {
+			ob_end_clean();
+			restore_error_handler();
+		}
+	}
+
+	/**
+	 * @return void
+	 */
+	public function testHostStatusResolvesMaintFromPluginRoot(): void {
+		$this->runHostStatus($this->fixtureRoot('cacti-root'));
+
+		$this->assertNotContains('ERROR: cannot include maint functions', CactiStubs::$log);
+	}
+
+	/**
+	 * @return void
+	 */
+	public function testHostStatusResolvesMaintFromIncludesLayout(): void {
+		$this->runHostStatus($this->fixtureRoot('cacti-root-maint-includes'));
+
+		$this->assertNotContains('ERROR: cannot include maint functions', CactiStubs::$log);
+	}
+
+	/**
+	 * @return void
+	 */
+	public function testHostStatusLogsWhenMaintFunctionsMissing(): void {
+		$this->runHostStatus($this->fixtureRoot('cacti-root-no-maint'));
+
+		$this->assertContains('ERROR: cannot include maint functions', CactiStubs::$log);
+	}
+}