diff --git a/inc/class-insert-post-handler.php b/inc/class-insert-post-handler.php
new file mode 100644
index 0000000..0399660
--- /dev/null
+++ b/inc/class-insert-post-handler.php
@@ -0,0 +1,91 @@
+<?php
+/**
+ * Handler for encapsulating hook callbacks called when inserting posts.
+ *
+ * @package authorship
+ */
+
+declare( strict_types=1 );
+
+namespace Authorship;
+
+use Exception;
+use WP_Post;
+
+/**
+ * Core class for encapsulating hook callbacks called when inserting posts.
+ *
+ * This is needed because state is passed between the callbacks.
+ */
+class InsertPostHandler {
+	/**
+	 * @var array<mixed>
+	 */
+	private $postarr = [];
+
+	/**
+	 * Filters slashed post data just before it is inserted into the database.
+	 *
+	 * @param mixed[] $data                An array of slashed, sanitized, and processed post data.
+	 * @param mixed[] $postarr             An array of sanitized (and slashed) but otherwise unmodified post data.
+	 * @param mixed   $unsanitized_postarr An array (or object that implements array access, like a WP_Post) of
+	 *                                     slashed yet _unsanitized_ and unprocessed post data as originally passed
+	 *                                     to wp_insert_post().
+	 * @return mixed[] An array of slashed, sanitized, and processed post data.
+	 */
+	function filter_wp_insert_post_data( array $data, array $postarr, $unsanitized_postarr ) : array {
+		// Make sure the unsanitized post array is actually an array. Core sometimes passes it as a WP_Post object.
+		$this->postarr = (array) $unsanitized_postarr;
+
+		return $data;
+	}
+
+	/**
+	 * Fires once a post has been saved.
+	 *
+	 * @param int     $post_ID Post ID.
+	 * @param WP_Post $post    Post object.
+	 * @param bool    $update  Whether this is an existing post being updated.
+	 */
+	function action_wp_insert_post( int $post_ID, WP_Post $post, bool $update ) : void {
+		$unsanitized_postarr = $this->postarr;
+
+		$this->postarr = [];
+
+		if ( isset( $unsanitized_postarr['tax_input'] ) && ! empty( $unsanitized_postarr['tax_input'][ TAXONOMY ] ) ) {
+			return;
+		}
+
+		$existing_authors = get_authors( $post );
+
+		if ( $update && ! isset( $unsanitized_postarr[ POSTS_PARAM ] ) && $existing_authors ) {
+			return;
+		}
+
+		if ( isset( $unsanitized_postarr[ POSTS_PARAM ] ) ) {
+			$authors = $unsanitized_postarr[ POSTS_PARAM ];
+		} else {
+			/**
+			 * Set the default authorship author. Defaults to the orignal post author.
+			 *
+			 * @param array $authors Authors to add to a post on insert if none have been passed. Default to post author.
+			 * @param WP_Post $post Post object.
+			 */
+			$authors = array_filter( apply_filters(
+				'authorship_default_author',
+				[ isset( $unsanitized_postarr['post_author'] ) ? $unsanitized_postarr['post_author'] : null ],
+				$post
+			) );
+		}
+
+		if ( empty( $authors ) ) {
+			return;
+		}
+
+		try {
+			set_authors( $post, wp_parse_id_list( $authors ) );
+		} catch ( Exception $e ) {
+			// Nothing at the moment.
+		}
+	}
+}
diff --git a/inc/namespace.php b/inc/namespace.php
index 0a840f6..0d360d3 100644
--- a/inc/namespace.php
+++ b/inc/namespace.php
@@ -333,79 +333,6 @@ function filter_rest_request_after_callbacks( $result, array $handler, WP_REST_R
 	return $result;
 }
 
-class InsertPostHandler {
-	/**
-	 * @var array<mixed>
-	 */
-	private $postarr = [];
-
-	/**
-	 * Filters slashed post data just before it is inserted into the database.
-	 *
-	 * @param mixed[] $data                An array of slashed, sanitized, and processed post data.
-	 * @param mixed[] $postarr             An array of sanitized (and slashed) but otherwise unmodified post data.
-	 * @param mixed   $unsanitized_postarr An array (or object that implements array access, like a WP_Post) of
-	 *                                     slashed yet _unsanitized_ and unprocessed post data as originally passed
-	 *                                     to wp_insert_post().
-	 * @return mixed[] An array of slashed, sanitized, and processed post data.
-	 */
-	function filter_wp_insert_post_data( array $data, array $postarr, $unsanitized_postarr ) : array {
-		// Make sure the unsanitized post array is actually an array. Core sometimes passes it as a WP_Post object.
-		$this->postarr = (array) $unsanitized_postarr;
-
-		return $data;
-	}
-
-	/**
-	 * Fires once a post has been saved.
-	 *
-	 * @param int     $post_ID Post ID.
-	 * @param WP_Post $post    Post object.
-	 * @param bool    $update  Whether this is an existing post being updated.
-	 */
-	function action_wp_insert_post( int $post_ID, WP_Post $post, bool $update ) : void {
-		$unsanitized_postarr = $this->postarr;
-
-		$this->postarr = [];
-
-		if ( isset( $unsanitized_postarr['tax_input'] ) && ! empty( $unsanitized_postarr['tax_input'][ TAXONOMY ] ) ) {
-			return;
-		}
-
-		$existing_authors = get_authors( $post );
-
-		if ( $update && ! isset( $unsanitized_postarr[ POSTS_PARAM ] ) && $existing_authors ) {
-			return;
-		}
-
-		if ( isset( $unsanitized_postarr[ POSTS_PARAM ] ) ) {
-			$authors = $unsanitized_postarr[ POSTS_PARAM ];
-		} else {
-			/**
-			 * Set the default authorship author. Defaults to the orignal post author.
-			 *
-			 * @param array $authors Authors to add to a post on insert if none have been passed. Default to post author.
-			 * @param WP_Post $post Post object.
-			 */
-			$authors = array_filter( apply_filters(
-				'authorship_default_author',
-				[ isset( $unsanitized_postarr['post_author'] ) ? $unsanitized_postarr['post_author'] : null ],
-				$post
-			) );
-		}
-
-		if ( empty( $authors ) ) {
-			return;
-		}
-
-		try {
-			set_authors( $post, wp_parse_id_list( $authors ) );
-		} catch ( Exception $e ) {
-			// Nothing at the moment.
-		}
-	}
-}
-
 /**
  * Adds the authorship field to the REST API for post objects.
  *
diff --git a/plugin.php b/plugin.php
index 4369d15..80837d6 100644
--- a/plugin.php
+++ b/plugin.php
@@ -43,6 +43,7 @@
 require_once __DIR__ . '/inc/namespace.php';
 require_once __DIR__ . '/inc/taxonomy.php';
 require_once __DIR__ . '/inc/class-users-controller.php';
+require_once __DIR__ . '/inc/class-insert-post-handler.php';
 require_once __DIR__ . '/inc/template.php';
 
 if ( is_admin() ) {