diff --git a/apps/backend/src/application/auth/auth.service.ts b/apps/backend/src/application/auth/auth.service.ts
index 040ff1b..17f20f8 100644
--- a/apps/backend/src/application/auth/auth.service.ts
+++ b/apps/backend/src/application/auth/auth.service.ts
@@ -70,6 +70,12 @@ export class AuthService {
     organizationData?: RegisterOrganizationDto,
     invitationRole?: string
   ): Promise<{ accessToken: string; refreshToken: string; user: any }> {
+    // Emails are stored lowercase (enforced by the chk_users_email DB CHECK
+    // constraint), so normalize before any lookup or insert. Without this, an
+    // address containing uppercase letters fails the user INSERT after the
+    // organization has already been created — leaving an orphaned organization.
+    email = email.trim().toLowerCase();
+
     this.logger.log(`Registering new user: ${email}`);
 
     const existingUser = await this.userRepository.findByEmail(email);
@@ -90,6 +96,9 @@ export class AuthService {
     // 2. If organizationData is provided (new user), create a new organization
     // 3. Otherwise, use default organization
     const finalOrganizationId = await this.resolveOrganizationId(organizationId, organizationData);
+    // Track whether a brand-new organization was created for this registration,
+    // so it can be rolled back if the subsequent user creation fails.
+    const createdNewOrg = !organizationId && !!organizationData;
 
     // Determine role:
     // - If invitation role is provided (invited user), use it
@@ -121,7 +130,28 @@ export class AuthService {
       role: userRole,
     });
 
-    const savedUser = await this.userRepository.save(user);
+    let savedUser: User;
+    try {
+      savedUser = await this.userRepository.save(user);
+    } catch (err) {
+      // The organization is created before the user (non-atomic flow). If the
+      // user INSERT fails, roll the organization back so a retry isn't blocked
+      // by an orphaned organization ("name already exists").
+      if (createdNewOrg) {
+        try {
+          await this.organizationRepository.deleteById(finalOrganizationId);
+          this.logger.warn(
+            `Rolled back orphaned organization ${finalOrganizationId} after failed user creation`
+          );
+        } catch (cleanupErr) {
+          this.logger.error(
+            `Failed to roll back organization ${finalOrganizationId}`,
+            cleanupErr as Error
+          );
+        }
+      }
+      throw err;
+    }
 
     // Allocate a license for the new user
     try {
@@ -158,6 +188,7 @@ export class AuthService {
     password: string,
     rememberMe = false
   ): Promise<{ accessToken: string; refreshToken: string; user: any }> {
+    email = email.trim().toLowerCase();
     this.logger.log(`Login attempt for: ${email}`);
 
     const user = await this.userRepository.findByEmail(email);