diff --git a/src/Access/Authentication.cpp b/src/Access/Authentication.cpp
index 7174c66d4b1..e38bd5abfe5 100644
--- a/src/Access/Authentication.cpp
+++ b/src/Access/Authentication.cpp
@@ -15,7 +15,6 @@ namespace DB
 {
 namespace ErrorCodes
 {
-    extern const int NOT_IMPLEMENTED;
     extern const int LOGICAL_ERROR;
 }