diff --git a/src/main/java/aplp/backend/core/common/exception/ErrorCode.java b/src/main/java/aplp/backend/core/common/exception/ErrorCode.java
index 82d3702..ccf4381 100644
--- a/src/main/java/aplp/backend/core/common/exception/ErrorCode.java
+++ b/src/main/java/aplp/backend/core/common/exception/ErrorCode.java
@@ -10,6 +10,7 @@ public enum ErrorCode {
     INVALID_REFRESH_TOKEN(401),
     ACCESS_DENIED(403),
     EMAIL_ALREADY_EXISTS(409),
+    USERNAME_ALREADY_EXISTS(409),
     USER_NOT_FOUND(404),
     LEARNER_NOT_FOUND(404),
     INTERNAL_ERROR(500);