diff --git a/backend/crates/domain/src/lib.rs b/backend/crates/domain/src/lib.rs
index c392d07..df889e5 100644
--- a/backend/crates/domain/src/lib.rs
+++ b/backend/crates/domain/src/lib.rs
@@ -48,7 +48,7 @@ impl User {
     // Constructor with validation
     pub fn new(id: Uuid, username: String, email: String) -> Result<Self> {
         if username.trim().is_empty() {
-            return Err(DomainError::InvalidInput("Username cannot be empty".to_string()));
+            return Err(DomainError::InvalidInput("Username cannot be empty.".to_string()));
         }
         
         let now = Utc::now();