diff --git a/lib/hexo/index.js b/lib/hexo/index.js
index a14819b257..41d9ffa50b 100644
--- a/lib/hexo/index.js
+++ b/lib/hexo/index.js
@@ -200,15 +200,9 @@ class Hexo extends EventEmitter {
       return db.model('Page').find(query);
     });
 
-    locals.set('categories', () => {
-      // Ignore categories with zero posts
-      return db.model('Category').filter(category => category.length);
-    });
+    locals.set('categories', () => db.model('Category'));
 
-    locals.set('tags', () => {
-      // Ignore tags with zero posts
-      return db.model('Tag').filter(tag => tag.length);
-    });
+    locals.set('tags', () => db.model('Tag'));
 
     locals.set('data', () => {
       const obj = {};
diff --git a/lib/models/category.js b/lib/models/category.js
index 2da88d37f8..5c535799a6 100644
--- a/lib/models/category.js
+++ b/lib/models/category.js
@@ -52,7 +52,9 @@ module.exports = ctx => {
   });
 
   Category.virtual('length').get(function() {
-    return this.posts.length;
+    const PostCategory = ctx.model('PostCategory');
+
+    return PostCategory.find({category_id: this._id}).length;
   });
 
   // Check whether a category exists
diff --git a/lib/models/post.js b/lib/models/post.js
index 4f8eff6843..4cb28421e3 100644
--- a/lib/models/post.js
+++ b/lib/models/post.js
@@ -71,7 +71,17 @@ module.exports = ctx => {
     return Tag.find({_id: {$in: ids}});
   });
 
+  Post.method('notPublished', function() {
+    // The same condition as ctx._bindLocals
+    return (!ctx.config.future && this.date > Date.now()) || (!ctx._showDrafts() && this.published === false);
+  });
+
   Post.method('setTags', function(tags) {
+    if (this.notPublished()) {
+      // Ignore tags of draft posts
+      // If the post is unpublished then the tag needs to be removed, thus the function cannot be returned early here
+      tags = [];
+    }
     tags = removeEmptyTag(tags);
 
     const PostTag = ctx.model('PostTag');
@@ -119,6 +129,9 @@ module.exports = ctx => {
   });
 
   Post.method('setCategories', function(cats) {
+    if (this.notPublished()) {
+      cats = [];
+    }
     // Remove empty categories, preserving hierarchies
     cats = cats.filter(cat => {
       return Array.isArray(cat) || (cat != null && cat !== '');
diff --git a/lib/models/tag.js b/lib/models/tag.js
index 807836d73f..7f6245c861 100644
--- a/lib/models/tag.js
+++ b/lib/models/tag.js
@@ -43,7 +43,11 @@ module.exports = ctx => {
   });
 
   Tag.virtual('length').get(function() {
-    return this.posts.length;
+    // Note: this.posts.length is also working
+    // But it's slow because `find` has to iterate over all posts
+    const PostTag = ctx.model('PostTag');
+
+    return PostTag.find({tag_id: this._id}).length;
   });
 
   // Check whether a tag exists
diff --git a/lib/plugins/helper/list_categories.js b/lib/plugins/helper/list_categories.js
index 182ca4ed5d..51455f2294 100644
--- a/lib/plugins/helper/list_categories.js
+++ b/lib/plugins/helper/list_categories.js
@@ -29,7 +29,7 @@ function listCategoriesHelper(categories, options) {
       query.parent = {$exists: false};
     }
 
-    return categories.find(query).sort(orderby, order).filter(cat => cat.length);
+    return categories.find(query).sort(orderby, order);
   };
 
   const hierarchicalList = (level, parent) => {
diff --git a/lib/plugins/helper/list_tags.js b/lib/plugins/helper/list_tags.js
index f9970f6c0b..c75626f720 100644
--- a/lib/plugins/helper/list_tags.js
+++ b/lib/plugins/helper/list_tags.js
@@ -47,9 +47,6 @@ function listTagsHelper(tags, options) {
   // Sort the tags
   tags = tags.sort(orderby, order);
 
-  // Ignore tags with zero posts
-  tags = tags.filter(tag => tag.length);
-
   // Limit the number of tags
   if (options.amount) tags = tags.limit(options.amount);
 
diff --git a/test/scripts/models/category.js b/test/scripts/models/category.js
index c48198674d..96553e68ca 100644
--- a/test/scripts/models/category.js
+++ b/test/scripts/models/category.js
@@ -191,6 +191,8 @@ describe('Category', () => {
 
     // draft on
     hexo.config.render_drafts = true;
+
+    await Promise.all(posts.map(post => post.setCategories(['foo'])));
     hexo.locals.invalidate();
     cat = Category.findOne({name: 'foo'});
     cat.posts.map(mapper).should.eql(posts.map(mapper));
@@ -227,6 +229,8 @@ describe('Category', () => {
 
     // future off
     hexo.config.future = false;
+
+    await Promise.all(posts.map(post => post.setCategories(['foo'])));
     hexo.locals.invalidate();
     cat = Category.findOne({name: 'foo'});
     cat.posts.eq(0)._id.should.eql(posts[0]._id);
diff --git a/test/scripts/models/tag.js b/test/scripts/models/tag.js
index 871f766082..5e77692da5 100644
--- a/test/scripts/models/tag.js
+++ b/test/scripts/models/tag.js
@@ -172,6 +172,7 @@ describe('Tag', () => {
 
     // draft on
     hexo.config.render_drafts = true;
+    await Promise.all(posts.map(post => post.setTags(['foo'])));
     tag = Tag.findOne({name: 'foo'});
     hexo.locals.invalidate();
     tag.posts.map(mapper).should.eql(posts.map(mapper));
@@ -206,6 +207,7 @@ describe('Tag', () => {
 
     // future off
     hexo.config.future = false;
+    await Promise.all(posts.map(post => post.setTags(['foo'])));
     hexo.locals.invalidate();
     tag = Tag.findOne({name: 'foo'});
     tag.posts.eq(0)._id.should.eql(posts[0]._id);