diff --git a/public/openapi/components/schemas/TopicObject.yaml b/public/openapi/components/schemas/TopicObject.yaml
index 9481d81305..69662e0080 100644
--- a/public/openapi/components/schemas/TopicObject.yaml
+++ b/public/openapi/components/schemas/TopicObject.yaml
@@ -26,6 +26,8 @@ TopicObject:
       type: number
     viewcount:
       type: number
+    postercount:
+      type: number
     teaserPid:
       oneOf:
         - type: number
diff --git a/public/openapi/read/topic/tid/id.yaml b/public/openapi/read/topic/tid/id.yaml
index 4c83350b37..cdc638a1f5 100644
--- a/public/openapi/read/topic/tid/id.yaml
+++ b/public/openapi/read/topic/tid/id.yaml
@@ -36,6 +36,8 @@ get:
                 type: number
               lastposttime:
                 type: number
+              postercount:
+                type: number
               postcount:
                 type: number
               viewcount:
diff --git a/public/openapi/read/topic/topic_id/slug/post_index.yaml b/public/openapi/read/topic/topic_id/slug/post_index.yaml
index 6d520ba1c1..d9374eff97 100644
--- a/public/openapi/read/topic/topic_id/slug/post_index.yaml
+++ b/public/openapi/read/topic/topic_id/slug/post_index.yaml
@@ -53,7 +53,7 @@ get:
                     type: number
                   viewcount:
                     type: number
-                  posterCount:
+                  postercount:
                     type: number
                     description: The number of unique users who made a post in this topic
                   mainPid:
diff --git a/src/topics/data.js b/src/topics/data.js
index 6b73163b4c..06476755ef 100644
--- a/src/topics/data.js
+++ b/src/topics/data.js
@@ -10,7 +10,7 @@ const plugins = require('../plugins');
 
 const intFields = [
 	'tid', 'cid', 'uid', 'mainPid', 'postcount',
-	'viewcount', 'deleted', 'locked', 'pinned',
+	'viewcount', 'postercount', 'deleted', 'locked', 'pinned',
 	'timestamp', 'upvotes', 'downvotes', 'lastposttime',
 	'deleterUid',
 ];
diff --git a/src/topics/index.js b/src/topics/index.js
index 3ed54ce0e8..418797a3f7 100644
--- a/src/topics/index.js
+++ b/src/topics/index.js
@@ -146,7 +146,6 @@ Topics.getTopicWithPosts = async function (topicData, set, uid, start, stop, rev
 		deleter,
 		merger,
 		related,
-		posterCount,
 	] = await Promise.all([
 		getMainPostAndReplies(topicData, set, uid, start, stop, reverse),
 		categories.getCategoryData(topicData.cid),
@@ -158,7 +157,6 @@ Topics.getTopicWithPosts = async function (topicData, set, uid, start, stop, rev
 		getDeleter(topicData),
 		getMerger(topicData),
 		getRelated(topicData, uid),
-		db.sortedSetCard('tid:' + topicData.tid + ':posters'),
 	]);
 
 	topicData.posts = posts;
@@ -181,7 +179,6 @@ Topics.getTopicWithPosts = async function (topicData, set, uid, start, stop, rev
 		topicData.mergedTimestampISO = utils.toISOString(topicData.mergedTimestamp);
 	}
 	topicData.related = related || [];
-	topicData.posterCount = posterCount;
 	topicData.unreplied = topicData.postcount === 1;
 	topicData.icons = [];
 
diff --git a/src/topics/posts.js b/src/topics/posts.js
index 7ecbf1fb86..883d66907f 100644
--- a/src/topics/posts.js
+++ b/src/topics/posts.js
@@ -174,6 +174,8 @@ module.exports = function (Topics) {
 		}
 		await Topics.increasePostCount(tid);
 		await db.sortedSetIncrBy('tid:' + tid + ':posters', 1, postData.uid);
+		const posterCount = await db.sortedSetCard('tid:' + tid + ':posters');
+		await Topics.setTopicField(tid, 'postercount', posterCount);
 		await Topics.updateTeaser(tid);
 	};
 
@@ -184,6 +186,9 @@ module.exports = function (Topics) {
 		], postData.pid);
 		await Topics.decreasePostCount(tid);
 		await db.sortedSetIncrBy('tid:' + tid + ':posters', -1, postData.uid);
+		await db.sortedSetsRemoveRangeByScore(['tid:' + tid + ':posters'], '-inf', 0);
+		const posterCount = await db.sortedSetCard('tid:' + tid + ':posters');
+		await Topics.setTopicField(tid, 'postercount', posterCount);
 		await Topics.updateTeaser(tid);
 	};
 
diff --git a/src/upgrades/1.15.0/topic_poster_count.js b/src/upgrades/1.15.0/topic_poster_count.js
new file mode 100644
index 0000000000..b07111c800
--- /dev/null
+++ b/src/upgrades/1.15.0/topic_poster_count.js
@@ -0,0 +1,29 @@
+'use strict';
+
+const db = require('../../database');
+
+const batch = require('../../batch');
+
+module.exports = {
+	name: 'Store poster count in topic hash',
+	timestamp: Date.UTC(2020, 9, 24),
+	method: async function () {
+		const progress = this.progress;
+
+		await batch.processSortedSet('topics:tid', async function (tids) {
+			progress.incr(tids.length);
+			const keys = tids.map(tid => 'tid:' + tid + ':posters');
+			await db.sortedSetsRemoveRangeByScore(keys, '-inf', 0);
+			const counts = await db.sortedSetsCard(keys);
+			for (let i = 0; i < tids.length; i++) {
+				if (counts[i] > 0) {
+					// eslint-disable-next-line no-await-in-loop
+					await db.setObjectField('topic:' + tids[i], 'postercount', counts[i]);
+				}
+			}
+		}, {
+			progress: progress,
+			batchSize: 500,
+		});
+	},
+};