diff --git a/app/serializers/post_revision_serializer.rb b/app/serializers/post_revision_serializer.rb
index 543ad073a2b..5a6939dfa49 100644
--- a/app/serializers/post_revision_serializer.rb
+++ b/app/serializers/post_revision_serializer.rb
@@ -279,7 +279,7 @@ class PostRevisionSerializer < ApplicationSerializer
   end
 
   def filter_tags(tags)
-    tags - hidden_tags
+    tags.is_a?(Array) && tags.any? ? tags - hidden_tags : tags
   end
 
   def filter_category_id(category_id)
diff --git a/spec/serializers/post_revision_serializer_spec.rb b/spec/serializers/post_revision_serializer_spec.rb
index 0d526ad4b02..bea000255f5 100644
--- a/spec/serializers/post_revision_serializer_spec.rb
+++ b/spec/serializers/post_revision_serializer_spec.rb
@@ -41,6 +41,16 @@ RSpec.describe PostRevisionSerializer do
     end
   end
 
+  it "handles tags not being an array" do
+    pr = Fabricate(:post_revision, post: post, modifications: { "tags" => ["[]", ""] })
+
+    json =
+      PostRevisionSerializer.new(pr, scope: Guardian.new(Fabricate(:user)), root: false).as_json
+
+    expect(json[:tags_changes][:previous]).to eq("[]")
+    expect(json[:tags_changes][:current]).to eq([])
+  end
+
   context "with hidden tags" do
     fab!(:public_tag) { Fabricate(:tag, name: "public") }
     fab!(:public_tag2) { Fabricate(:tag, name: "visible") }