diff --git a/app/controllers/oidc_controller.rb b/app/controllers/oidc_controller.rb
index 29144db..cbea16c 100644
--- a/app/controllers/oidc_controller.rb
+++ b/app/controllers/oidc_controller.rb
@@ -657,9 +657,28 @@ class OidcController < ApplicationController
     end
 
     # Profile claims (only if 'profile' scope requested)
+    # Per OIDC Core spec section 5.4, all profile claims SHOULD be returned
     if requested_scopes.include?("profile")
-      claims[:preferred_username] = user.email_address
+      # Use username if available, otherwise email as preferred_username
+      claims[:preferred_username] = user.username.presence || user.email_address
+      # Name: use stored name or fall back to email
       claims[:name] = user.name.presence || user.email_address
+
+      # Standard profile claims we don't store - set to nil (optional per spec)
+      claims[:given_name] = nil
+      claims[:family_name] = nil
+      claims[:middle_name] = nil
+      claims[:nickname] = nil
+      claims[:profile] = nil
+      claims[:picture] = nil
+      claims[:website] = nil
+      claims[:gender] = nil
+      claims[:birthdate] = nil
+      claims[:zoneinfo] = nil
+      claims[:locale] = nil
+
+      # Time the user's information was last updated
+      claims[:updated_at] = user.updated_at.to_i
     end
 
     # Groups claim (only if 'groups' scope requested)
diff --git a/test/controllers/oidc_userinfo_controller_test.rb b/test/controllers/oidc_userinfo_controller_test.rb
index f749b5f..b7c4b4a 100644
--- a/test/controllers/oidc_userinfo_controller_test.rb
+++ b/test/controllers/oidc_userinfo_controller_test.rb
@@ -115,9 +115,25 @@ class OidcUserinfoControllerTest < ActionDispatch::IntegrationTest
     # Required claims
     assert json["sub"].present?
 
-    # Profile claims should be present
-    assert_equal @user.email_address, json["preferred_username"], "Should include preferred_username with profile scope"
-    assert json["name"].present?, "Should include name with profile scope"
+    # All standard profile claims should be present (per OIDC Core spec section 5.4)
+    # Some may be null if we don't have the data, but the keys should exist
+    assert json.key?("name"), "Should include name claim"
+    assert json.key?("given_name"), "Should include given_name claim (may be null)"
+    assert json.key?("family_name"), "Should include family_name claim (may be null)"
+    assert json.key?("middle_name"), "Should include middle_name claim (may be null)"
+    assert json.key?("nickname"), "Should include nickname claim (may be null)"
+    assert json.key?("preferred_username"), "Should include preferred_username claim"
+    assert json.key?("profile"), "Should include profile claim (may be null)"
+    assert json.key?("picture"), "Should include picture claim (may be null)"
+    assert json.key?("website"), "Should include website claim (may be null)"
+    assert json.key?("gender"), "Should include gender claim (may be null)"
+    assert json.key?("birthdate"), "Should include birthdate claim (may be null)"
+    assert json.key?("zoneinfo"), "Should include zoneinfo claim (may be null)"
+    assert json.key?("locale"), "Should include locale claim (may be null)"
+    assert json.key?("updated_at"), "Should include updated_at claim"
+
+    # Verify preferred_username is using username or email
+    assert json["preferred_username"].present?, "preferred_username should have a value"
 
     # Email claims should NOT be present
     assert_nil json["email"], "Should not include email without email scope"