diff --git a/plugins/poll/db/migrate/20230614041219_delete_duplicate_poll_votes.rb b/plugins/poll/db/migrate/20230614041219_delete_duplicate_poll_votes.rb
new file mode 100644
index 00000000000..4b1fb71a195
--- /dev/null
+++ b/plugins/poll/db/migrate/20230614041219_delete_duplicate_poll_votes.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class DeleteDuplicatePollVotes < ActiveRecord::Migration[7.0]
+  def up
+    execute <<~SQL
+      DELETE FROM poll_votes
+      WHERE (poll_id, user_id, updated_at) NOT IN (
+        SELECT poll_id, user_id, MAX(updated_at)
+        FROM poll_votes
+        GROUP BY poll_id, user_id
+      )
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end
diff --git a/plugins/poll/plugin.rb b/plugins/poll/plugin.rb
index be2cb91810c..9efaa93f2ef 100644
--- a/plugins/poll/plugin.rb
+++ b/plugins/poll/plugin.rb
@@ -169,7 +169,22 @@ after_initialize do
   end
 
   on(:merging_users) do |source_user, target_user|
-    PollVote.where(user_id: source_user.id).update_all(user_id: target_user.id)
+    DB.exec(<<-SQL, source_user_id: source_user.id, target_user_id: target_user.id)
+      DELETE FROM poll_votes
+      WHERE poll_id IN (
+        SELECT poll_id
+        FROM poll_votes
+        WHERE user_id = :source_user_id
+        INTERSECT
+        SELECT poll_id
+        FROM poll_votes
+        WHERE user_id = :target_user_id
+      ) AND user_id = :source_user_id;
+
+      UPDATE poll_votes
+      SET user_id = :target_user_id
+      WHERE user_id = :source_user_id;
+    SQL
   end
 
   add_to_class(:topic_view, :polls) do
diff --git a/plugins/poll/spec/fabricators/poll_fabricator.rb b/plugins/poll/spec/fabricators/poll_fabricator.rb
new file mode 100644
index 00000000000..33049dfada0
--- /dev/null
+++ b/plugins/poll/spec/fabricators/poll_fabricator.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+Fabricator(:poll) do
+  post
+  name { sequence(:name) { |i| "Poll #{i}" } }
+end
+
+Fabricator(:poll_option) do
+  poll
+  html { sequence(:html) { |i| "Poll Option #{i}" } }
+  digest { sequence(:digest) { |i| "#{i}" } }
+end
+
+Fabricator(:poll_vote) do
+  poll
+  poll_option
+  user
+end
diff --git a/plugins/poll/spec/integration/user_merger_spec.rb b/plugins/poll/spec/integration/user_merger_spec.rb
new file mode 100644
index 00000000000..8c5f14f9ffd
--- /dev/null
+++ b/plugins/poll/spec/integration/user_merger_spec.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+RSpec.describe UserMerger do
+  fab!(:target_user) { Fabricate(:user, username: "galahad", email: "galahad@knights.com") }
+  fab!(:source_user) { Fabricate(:user, username: "lancelot", email: "lancelot@knights.com") }
+  fab!(:poll) { Fabricate(:poll) }
+
+  it "deletes source_user vote if target_user already voted" do
+    Fabricate(:poll_vote, poll: poll, user: target_user)
+    Fabricate(:poll_vote, poll: poll, user: source_user)
+
+    DiscourseEvent.trigger(:merging_users, source_user, target_user)
+
+    expect(PollVote.where(user: source_user).count).to eq(0)
+  end
+
+  it "keeps only target_user vote if duplicate" do
+    target_vote = Fabricate(:poll_vote, poll: poll, user: target_user)
+    Fabricate(:poll_vote, poll: poll, user: source_user)
+
+    DiscourseEvent.trigger(:merging_users, source_user, target_user)
+
+    expect(PollVote.where(user: target_user).to_json).to eq([target_vote].to_json)
+  end
+
+  it "reassigns source_user vote to target_user if not duplicate" do
+    Fabricate(:poll_vote, poll: poll, user: source_user)
+
+    expect { DiscourseEvent.trigger(:merging_users, source_user, target_user) }.to change(
+      PollVote.where(user: target_user),
+      :count,
+    ).from(0).to(1)
+  end
+
+  it "keeps any existing target_user votes" do
+    Fabricate(:poll_vote, poll: poll, user: target_user)
+
+    expect { DiscourseEvent.trigger(:merging_users, source_user, target_user) }.to not_change(
+      PollVote.where(user: target_user),
+      :count,
+    )
+  end
+end