diff --git a/dbms/src/Storages/MergeTree/MergeTreeDataMergerMutator.cpp b/dbms/src/Storages/MergeTree/MergeTreeDataMergerMutator.cpp
index 62a5af46f6d..40c34960c60 100644
--- a/dbms/src/Storages/MergeTree/MergeTreeDataMergerMutator.cpp
+++ b/dbms/src/Storages/MergeTree/MergeTreeDataMergerMutator.cpp
@@ -56,7 +56,6 @@ namespace ErrorCodes
     extern const int DIRECTORY_ALREADY_EXISTS;
     extern const int LOGICAL_ERROR;
     extern const int ABORTED;
-    extern const int UNKNOWN_MUTATION_COMMAND;
 }