diff --git a/.github/changelog/3138-from-description b/.github/changelog/3138-from-description
new file mode 100644
index 0000000000..16f0a5198b
--- /dev/null
+++ b/.github/changelog/3138-from-description
@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Fix cleanup jobs silently doing nothing on sites where purge retention options were not set.
diff --git a/includes/class-options.php b/includes/class-options.php
index 7fbe3a9162..b982098f13 100644
--- a/includes/class-options.php
+++ b/includes/class-options.php
@@ -35,6 +35,10 @@ public static function init() {
 		\add_filter( 'option_activitypub_support_post_types', array( self::class, 'support_post_types_ensure_array' ) );
 		\add_filter( 'option_activitypub_object_type', array( self::class, 'default_object_type' ) );
 
+		\add_filter( 'option_activitypub_outbox_purge_days', array( self::class, 'sanitize_purge_days' ) );
+		\add_filter( 'option_activitypub_inbox_purge_days', array( self::class, 'sanitize_purge_days' ) );
+		\add_filter( 'option_activitypub_ap_post_purge_days', array( self::class, 'sanitize_purge_days' ) );
+
 		\add_action( 'update_option_activitypub_relay_mode', array( self::class, 'relay_mode_changed' ), 10, 2 );
 	}
 
@@ -226,9 +230,12 @@ public static function register_settings() {
 			'activitypub_advanced',
 			'activitypub_outbox_purge_days',
 			array(
-				'type'        => 'integer',
-				'description' => 'Number of days to keep items in the Outbox.',
-				'default'     => 180,
+				'type'              => 'integer',
+				'description'       => 'Number of days to keep items in the Outbox.',
+				'default'           => ACTIVITYPUB_OUTBOX_PURGE_DAYS,
+				'sanitize_callback' => static function ( $value ) {
+					return \max( 1, \absint( $value ) );
+				},
 			)
 		);
 
@@ -236,9 +243,12 @@ public static function register_settings() {
 			'activitypub_advanced',
 			'activitypub_inbox_purge_days',
 			array(
-				'type'        => 'integer',
-				'description' => 'Number of days to keep items in the Inbox.',
-				'default'     => 180,
+				'type'              => 'integer',
+				'description'       => 'Number of days to keep items in the Inbox.',
+				'default'           => ACTIVITYPUB_INBOX_PURGE_DAYS,
+				'sanitize_callback' => static function ( $value ) {
+					return \max( 1, \absint( $value ) );
+				},
 			)
 		);
 
@@ -246,9 +256,12 @@ public static function register_settings() {
 			'activitypub_advanced',
 			'activitypub_ap_post_purge_days',
 			array(
-				'type'        => 'integer',
-				'description' => 'Number of days to keep remote posts.',
-				'default'     => 30,
+				'type'              => 'integer',
+				'description'       => 'Number of days to keep remote posts.',
+				'default'           => ACTIVITYPUB_AP_POST_PURGE_DAYS,
+				'sanitize_callback' => static function ( $value ) {
+					return \max( 1, \absint( $value ) );
+				},
 			)
 		);
 
@@ -660,6 +673,34 @@ public static function default_object_type( $value ) {
 		return $value;
 	}
 
+	/**
+	 * Sanitize purge day values.
+	 *
+	 * Ensures the value is a non-negative integer. Returns the
+	 * registered default when the stored value is empty or false
+	 * (option not properly set), but allows 0 to disable purging.
+	 *
+	 * @since unreleased
+	 *
+	 * @param mixed $value The stored option value.
+	 *
+	 * @return int The sanitized value.
+	 */
+	public static function sanitize_purge_days( $value ) {
+		if ( '' === $value || false === $value ) {
+			$filter   = \current_filter();
+			$defaults = array(
+				'option_activitypub_outbox_purge_days'  => ACTIVITYPUB_OUTBOX_PURGE_DAYS,
+				'option_activitypub_inbox_purge_days'   => ACTIVITYPUB_INBOX_PURGE_DAYS,
+				'option_activitypub_ap_post_purge_days' => ACTIVITYPUB_AP_POST_PURGE_DAYS,
+			);
+
+			return $defaults[ $filter ] ?? ACTIVITYPUB_OUTBOX_PURGE_DAYS;
+		}
+
+		return \max( 1, \absint( $value ) );
+	}
+
 	/**
 	 * Handle relay mode option changes.
 	 *
diff --git a/includes/class-scheduler.php b/includes/class-scheduler.php
index cd236a4b5b..1ec2ade8f2 100644
--- a/includes/class-scheduler.php
+++ b/includes/class-scheduler.php
@@ -387,24 +387,21 @@ public static function reprocess_outbox() {
 	 * Purge outbox items based on a schedule.
 	 */
 	public static function purge_outbox() {
-		$days = (int) \get_option( 'activitypub_outbox_purge_days', 180 );
-		Outbox::purge( $days );
+		Outbox::purge( \get_option( 'activitypub_outbox_purge_days', ACTIVITYPUB_OUTBOX_PURGE_DAYS ) );
 	}
 
 	/**
 	 * Purge inbox items based on a schedule.
 	 */
 	public static function purge_inbox() {
-		$days = (int) \get_option( 'activitypub_inbox_purge_days', 180 );
-		Inbox::purge( $days );
+		Inbox::purge( \get_option( 'activitypub_inbox_purge_days', ACTIVITYPUB_INBOX_PURGE_DAYS ) );
 	}
 
 	/**
 	 * Purge remote posts based on a schedule.
 	 */
 	public static function purge_ap_posts() {
-		$days = (int) \get_option( 'activitypub_ap_post_purge_days', 30 );
-		Remote_Posts::purge( $days );
+		Remote_Posts::purge( \get_option( 'activitypub_ap_post_purge_days', ACTIVITYPUB_AP_POST_PURGE_DAYS ) );
 	}
 
 	/**
diff --git a/includes/constants.php b/includes/constants.php
index 8c192d511b..2635d79f7a 100644
--- a/includes/constants.php
+++ b/includes/constants.php
@@ -109,3 +109,8 @@
  * @see https://github.com/tfredrich/RestApiTutorial.com/blob/master/content/advanced/responses/retries.md
  */
 define( 'ACTIVITYPUB_RETRY_ERROR_CODES', array( 408, 429, 500, 502, 503, 504 ) );
+
+// Default purge retention periods (in days).
+define( 'ACTIVITYPUB_OUTBOX_PURGE_DAYS', 180 );
+define( 'ACTIVITYPUB_INBOX_PURGE_DAYS', 180 );
+define( 'ACTIVITYPUB_AP_POST_PURGE_DAYS', 30 );
diff --git a/includes/wp-admin/class-health-check.php b/includes/wp-admin/class-health-check.php
index b96c76a0eb..a77184a021 100644
--- a/includes/wp-admin/class-health-check.php
+++ b/includes/wp-admin/class-health-check.php
@@ -386,13 +386,13 @@ public static function debug_information( $info ) {
 
 		$info['activitypub']['fields']['activitypub_outbox_purge_days'] = array(
 			'label'   => \__( 'Outbox Retention Period', 'activitypub' ),
-			'value'   => \esc_attr( (int) \get_option( 'activitypub_outbox_purge_days', 180 ) ),
+			'value'   => \esc_attr( (int) \get_option( 'activitypub_outbox_purge_days', ACTIVITYPUB_OUTBOX_PURGE_DAYS ) ),
 			'private' => false,
 		);
 
 		$info['activitypub']['fields']['activitypub_ap_post_purge_days'] = array(
 			'label'   => \__( 'Remote Posts Retention Period', 'activitypub' ),
-			'value'   => \esc_attr( (int) \get_option( 'activitypub_ap_post_purge_days', 30 ) ),
+			'value'   => \esc_attr( (int) \get_option( 'activitypub_ap_post_purge_days', ACTIVITYPUB_AP_POST_PURGE_DAYS ) ),
 			'private' => false,
 		);
 
diff --git a/tests/phpunit/tests/includes/class-test-options.php b/tests/phpunit/tests/includes/class-test-options.php
index 61279267d2..b97fc78b76 100644
--- a/tests/phpunit/tests/includes/class-test-options.php
+++ b/tests/phpunit/tests/includes/class-test-options.php
@@ -242,4 +242,56 @@ public function test_default_quote_policy_sanitizes_invalid_values() {
 		\update_option( 'activitypub_default_quote_policy', '' );
 		$this->assertEquals( ACTIVITYPUB_INTERACTION_POLICY_ANYONE, \get_option( 'activitypub_default_quote_policy' ) );
 	}
+
+	/**
+	 * Test purge days returns default when option is not set.
+	 *
+	 * @covers \Activitypub\Options::sanitize_purge_days
+	 */
+	public function test_purge_days_returns_default_when_unset() {
+		\delete_option( 'activitypub_outbox_purge_days' );
+
+		$this->assertEquals(
+			ACTIVITYPUB_OUTBOX_PURGE_DAYS,
+			\get_option( 'activitypub_outbox_purge_days', ACTIVITYPUB_OUTBOX_PURGE_DAYS )
+		);
+	}
+
+	/**
+	 * Test purge days does not allow zero.
+	 *
+	 * @covers \Activitypub\Options::sanitize_purge_days
+	 */
+	public function test_purge_days_does_not_allow_zero() {
+		Options::register_settings();
+
+		\update_option( 'activitypub_outbox_purge_days', 0 );
+		$this->assertGreaterThanOrEqual( 1, \get_option( 'activitypub_outbox_purge_days' ) );
+	}
+
+	/**
+	 * Test purge days returns default when stored value is empty string.
+	 *
+	 * @covers \Activitypub\Options::sanitize_purge_days
+	 */
+	public function test_purge_days_returns_default_for_empty_string() {
+		\update_option( 'activitypub_outbox_purge_days', '' );
+
+		$this->assertEquals(
+			ACTIVITYPUB_OUTBOX_PURGE_DAYS,
+			\get_option( 'activitypub_outbox_purge_days' )
+		);
+	}
+
+	/**
+	 * Test purge days sanitizes negative values.
+	 *
+	 * @covers \Activitypub\Options::sanitize_purge_days
+	 */
+	public function test_purge_days_sanitizes_negative() {
+		Options::register_settings();
+
+		\update_option( 'activitypub_outbox_purge_days', -5 );
+		$this->assertGreaterThanOrEqual( 1, \get_option( 'activitypub_outbox_purge_days' ) );
+	}
 }