diff --git a/src/Core/Settings.h b/src/Core/Settings.h
index b09e960da36..d8ba4f45b77 100644
--- a/src/Core/Settings.h
+++ b/src/Core/Settings.h
@@ -417,7 +417,7 @@ class IColumn;
     M(UInt64, multiple_joins_rewriter_version, 0, "Obsolete setting, does nothing. Will be removed after 2021-03-31", 0) \
     M(Bool, enable_debug_queries, false, "Enabled debug queries, but now is obsolete", 0) \
     M(Bool, allow_experimental_database_atomic, true, "Obsolete setting, does nothing. Will be removed after 2021-02-12", 0) \
-    M(UnionMode, union_default_mode, UnionMode::DISTINCT, "Set default Union Mode in SelectWithUnion query. Possible values: empty string, 'ALL', 'DISTINCT'. If empty, query without Union Mode will throw exception.", 0) \
+    M(UnionMode, union_default_mode, UnionMode::Unspecified, "Set default Union Mode in SelectWithUnion query. Possible values: empty string, 'ALL', 'DISTINCT'. If empty, query without Union Mode will throw exception.", 0) \
     M(Bool, optimize_aggregators_of_group_by_keys, true, "Eliminates min/max/any/anyLast aggregators of GROUP BY keys in SELECT section", 0) \
     M(Bool, optimize_group_by_function_keys, true, "Eliminates functions of other keys in GROUP BY section", 0) \