diff --git a/src/cache.ts b/src/cache.ts
index a636320..1404ae7 100644
--- a/src/cache.ts
+++ b/src/cache.ts
@@ -1114,7 +1114,7 @@ class Cache {
 
 					// Update user in cache with fresh data
 					await this.insertUser(
-						slackUser.id,
+						userId.toUpperCase(),
 						slackUser.real_name || slackUser.name || "Unknown",
 						slackUser.profile?.pronouns || "",
 						slackUser.profile?.image_512 || slackUser.profile?.image_192 || "",
diff --git a/src/handlers/index.ts b/src/handlers/index.ts
index 1d6035c..d7e73a3 100644
--- a/src/handlers/index.ts
+++ b/src/handlers/index.ts
@@ -89,8 +89,9 @@ export const handleGetUser: RouteHandlerWithAnalytics = async (
 			);
 		}
 
+		const resolvedId = userId.toUpperCase();
 		await cache.insertUser(
-			slackUser.id,
+			resolvedId,
 			slackUser.real_name || slackUser.name || "Unknown",
 			slackUser.profile?.pronouns || "",
 			slackUser.profile?.image_512 || slackUser.profile?.image_192 || "",
@@ -98,8 +99,8 @@ export const handleGetUser: RouteHandlerWithAnalytics = async (
 
 		recordAnalytics(200);
 		return Response.json({
-			id: slackUser.id,
-			userId: slackUser.id,
+			id: resolvedId,
+			userId: resolvedId,
 			displayName: slackUser.real_name || slackUser.name || "Unknown",
 			pronouns: slackUser.profile?.pronouns || "",
 			imageUrl:
diff --git a/src/slack.d.ts b/src/slack.d.ts
index 0c7d925..52161a5 100644
--- a/src/slack.d.ts
+++ b/src/slack.d.ts
@@ -64,6 +64,12 @@ export interface SlackUser {
 	is_app_user: boolean;
 	/** Whether user has two-factor auth enabled */
 	has_2fa: boolean;
+	/** Enterprise user info (present for enterprise grid users) */
+	enterprise_user?: {
+		id: string;
+		enterprise_id: string;
+		enterprise_name: string;
+	};
 }
 
 /**