diff --git a/app/models/user.rb b/app/models/user.rb
index cc0b712..5bd7282 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -5,7 +5,7 @@ class User < ApplicationRecord
   encrypts :slack_access_token, :github_access_token
 
   validates :slack_uid, uniqueness: true, allow_nil: true
-  validates :github_uid, uniqueness: true, allow_nil: true
+  validates :github_uid, uniqueness: { conditions: -> { where.not(github_access_token: nil) } }, allow_nil: true
   validates :timezone, inclusion: { in: TZInfo::Timezone.all_identifiers }, allow_nil: false
   validates :country_code, inclusion: { in: ISO3166::Country.codes }, allow_nil: true
 
@@ -365,8 +365,17 @@ class User < ApplicationRecord
     Rails.logger.info "GitHub user data: #{user_data.inspect}"
     Rails.logger.info "GitHub user ID type: #{user_data['id'].class}"
 
+    # Clear GitHub access tokens from any other users with this GitHub UID
+    github_uid = user_data["id"]
+    other_users = User.where(github_uid: github_uid).where.not(id: current_user.id).where.not(github_access_token: nil)
+
+    other_users.find_each do |user|
+      Rails.logger.info "Clearing GitHub token for User ##{user.id} (GitHub UID: #{github_uid}) - linking to new account"
+      user.update!(github_access_token: nil)
+    end
+
     # Update GitHub-specific fields
-    current_user.github_uid = user_data["id"]
+    current_user.github_uid = github_uid
     current_user.username ||= user_data["login"]
     current_user.github_username = user_data["login"]
     current_user.github_avatar_url = user_data["avatar_url"]
diff --git a/db/migrate/20250623135342_add_github_index_to_users.rb b/db/migrate/20250623135342_add_github_index_to_users.rb
new file mode 100644
index 0000000..6445097
--- /dev/null
+++ b/db/migrate/20250623135342_add_github_index_to_users.rb
@@ -0,0 +1,6 @@
+class AddGithubIndexToUsers < ActiveRecord::Migration[8.0]
+  def change
+    add_index :users, [ :github_uid, :github_access_token ],
+              name: "index_users_on_github_uid_and_access_token"
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index e9504e1..87c9594 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_06_18_170000) do
+ActiveRecord::Schema[8.0].define(version: 2025_06_23_135342) do
   create_schema "pganalyze"
 
   # These are extensions that must be enabled in order to support this database
@@ -494,6 +494,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_06_18_170000) do
     t.string "mailing_address_otc"
     t.boolean "allow_public_stats_lookup", default: true, null: false
     t.boolean "default_timezone_leaderboard", default: true, null: false
+    t.index ["github_uid", "github_access_token"], name: "index_users_on_github_uid_and_access_token"
     t.index ["slack_uid"], name: "index_users_on_slack_uid", unique: true
     t.index ["timezone"], name: "index_users_on_timezone"
   end