diff --git a/src/posts/data.js b/src/posts/data.js
index 20f1df2991..8edd4096e6 100644
--- a/src/posts/data.js
+++ b/src/posts/data.js
@@ -8,7 +8,7 @@ const activitypub = require('../activitypub');
 const utils = require('../utils');
 
 const intFields = [
-	'uid', 'pid', 'tid', 'toPid', 'deleted', 'timestamp',
+	'uid', 'pid', 'tid', 'deleted', 'timestamp',
 	'upvotes', 'downvotes', 'deleterUid', 'edited',
 	'replies', 'bookmarks',
 ];
@@ -62,7 +62,7 @@ function modifyPost(post, fields) {
 	const _intFields = [...intFields];
 
 	if (post) {
-		['pid', 'uid', 'tid', 'toPid'].forEach((prop) => {
+		['pid', 'uid', 'tid'].forEach((prop) => {
 			if (
 				post.hasOwnProperty(prop) &&
 				(activitypub.helpers.isUri(post[prop]) || validator.isUUID(String(post[prop])))
diff --git a/src/posts/summary.js b/src/posts/summary.js
index a07b8e2c67..6865372cef 100644
--- a/src/posts/summary.js
+++ b/src/posts/summary.js
@@ -44,6 +44,10 @@ module.exports = function (Posts) {
 			if (!uidToUser.hasOwnProperty(post.uid)) {
 				post.uid = 0;
 			}
+
+			// toPid is nullable so it is casted separately
+			post.toPid = utils.isNumber(post.toPid) ? parseInt(post.toPid, 10) : post.toPid;
+
 			post.user = uidToUser[post.uid];
 			Posts.overrideGuestHandle(post, post.handle);
 			post.handle = undefined;