diff --git a/backend/handlers/auth/local.go b/backend/handlers/auth/local.go
index 0cfdf9b..dd88af9 100644
--- a/backend/handlers/auth/local.go
+++ b/backend/handlers/auth/local.go
@@ -177,7 +177,7 @@ func RegisterHandler(w http.ResponseWriter, r *http.Request) {
 
 	// Validate referral code if provided
 	var referrerID *string
-	req.ReferralCode = strings.TrimSpace(req.ReferralCode)
+	req.ReferralCode = strings.ToLower(strings.TrimSpace(req.ReferralCode))
 	if req.ReferralCode != "" {
 		if len(req.ReferralCode) != 12 {
 			http.Error(w, "referral code must be exactly 12 characters", http.StatusBadRequest)