diff --git a/app/models/tag.rb b/app/models/tag.rb
index a856f7f75..25ac8e179 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -106,23 +106,43 @@ class Tag < ApplicationRecord
         Tag.where(name: tag_names).update_all("post_count = post_count - 1")
       end
 
-      def regenerate_post_counts!
-        sql = <<~SQL
+      # fix tags where the post count is non-zero but the tag isn't present on any posts.
+      def regenerate_nonexistent_post_counts!
+        Tag.find_by_sql(<<~SQL)
           UPDATE tags
-          SET post_count = COALESCE(true_count, 0)
+          SET post_count = 0
+          WHERE
+            post_count != 0
+            AND name NOT IN (
+              SELECT DISTINCT tag
+              FROM posts, unnest(string_to_array(tag_string, ' ')) AS tag
+              GROUP BY tag
+            )
+          RETURNING tags.*
+        SQL
+      end
+
+      # fix tags where the stored post count doesn't match the true post count.
+      def regenerate_incorrect_post_counts!
+        Tag.find_by_sql(<<~SQL)
+          UPDATE tags
+          SET post_count = true_count
           FROM (
             SELECT tag, COUNT(*) AS true_count
             FROM posts, unnest(string_to_array(tag_string, ' ')) AS tag
             GROUP BY tag
           ) true_counts
           WHERE
-            (tags.name = tag AND tags.post_count != true_count)
-            OR tags.post_count < 0
+            tags.name = tag AND tags.post_count != true_count
           RETURNING tags.*
         SQL
+      end
 
-        updated_tags = Tag.find_by_sql(sql)
-        updated_tags
+      def regenerate_post_counts!
+        tags = []
+        tags += regenerate_incorrect_post_counts!
+        tags += regenerate_nonexistent_post_counts!
+        tags
       end
     end
   end
diff --git a/test/unit/tag_test.rb b/test/unit/tag_test.rb
index e83da3942..9af0700bc 100644
--- a/test/unit/tag_test.rb
+++ b/test/unit/tag_test.rb
@@ -278,11 +278,14 @@ class TagTest < ActiveSupport::TestCase
     should "be fixed" do
       tag1 = FactoryBot.create(:tag, name: "touhou", post_count: -10)
       tag2 = FactoryBot.create(:tag, name: "bkub", post_count: 10)
+      tag3 = FactoryBot.create(:tag, name: "chen", post_count: 10)
       post = FactoryBot.create(:post, tag_string: "touhou bkub")
 
-      Tag.regenerate_post_counts!
+      tags = Tag.regenerate_post_counts!
+      assert_equal(3, tags.size)
       assert_equal(1, tag1.reload.post_count)
       assert_equal(1, tag2.reload.post_count)
+      assert_equal(0, tag3.reload.post_count)
     end
   end
 end