diff --git a/src/Storages/StorageMerge.h b/src/Storages/StorageMerge.h
index 7258f9cebaf..20460e95156 100644
--- a/src/Storages/StorageMerge.h
+++ b/src/Storages/StorageMerge.h
@@ -49,7 +49,7 @@ public:
         const ASTPtr & left_in_operand, ContextPtr query_context, const StorageMetadataPtr & metadata_snapshot) const override;
 
 private:
-    using DbToTableSetMap = std::unordered_map<String, std::unordered_set<String>>;
+    using DbToTableSetMap = std::map<String, std::set<String>>;
 
     std::optional<OptimizedRegularExpression> source_database_regexp;
     std::optional<OptimizedRegularExpression> source_table_regexp;
diff --git a/src/TableFunctions/TableFunctionMerge.cpp b/src/TableFunctions/TableFunctionMerge.cpp
index 7a905bf2ae7..40d0d1b7921 100644
--- a/src/TableFunctions/TableFunctionMerge.cpp
+++ b/src/TableFunctions/TableFunctionMerge.cpp
@@ -106,9 +106,12 @@ ColumnsDescription TableFunctionMerge::getActualTableStructure(ContextPtr contex
 {
     for (const auto & db_with_tables : getSourceDatabasesAndTables(context))
     {
-        auto storage = DatabaseCatalog::instance().tryGetTable(StorageID{db_with_tables.first, *db_with_tables.second.begin()}, context);
-        if (storage)
-            return ColumnsDescription{storage->getInMemoryMetadataPtr()->getColumns().getAllPhysical()};
+        for (const auto & table : db_with_tables.second)
+        {
+            auto storage = DatabaseCatalog::instance().tryGetTable(StorageID{db_with_tables.first, table}, context);
+            if (storage)
+                return ColumnsDescription{storage->getInMemoryMetadataPtr()->getColumns().getAllPhysical()};
+        }
     }
 
     throwNoTablesMatchRegexp(source_database_name_or_regexp, source_table_regexp);
@@ -130,7 +133,7 @@ StoragePtr TableFunctionMerge::executeImpl(const ASTPtr & /*ast_function*/, Cont
     return res;
 }
 
-NameSet
+TableFunctionMerge::TableSet
 TableFunctionMerge::getMatchedTablesWithAccess(const String & database_name, const String & table_regexp, const ContextPtr & context)
 {
     OptimizedRegularExpression table_re(table_regexp);
@@ -144,7 +147,7 @@ TableFunctionMerge::getMatchedTablesWithAccess(const String & database_name, con
     bool granted_show_on_all_tables = access->isGranted(AccessType::SHOW_TABLES, database_name);
     bool granted_select_on_all_tables = access->isGranted(AccessType::SELECT, database_name);
 
-    NameSet tables;
+    TableSet tables;
 
     for (auto it = database->getTablesIterator(context, table_name_match); it->isValid(); it->next())
     {
diff --git a/src/TableFunctions/TableFunctionMerge.h b/src/TableFunctions/TableFunctionMerge.h
index 438221ed95e..73b61f8eb79 100644
--- a/src/TableFunctions/TableFunctionMerge.h
+++ b/src/TableFunctions/TableFunctionMerge.h
@@ -20,11 +20,12 @@ private:
     StoragePtr executeImpl(const ASTPtr & ast_function, ContextPtr context, const std::string & table_name, ColumnsDescription cached_columns) const override;
     const char * getStorageTypeName() const override { return "Merge"; }
 
-    using DbToTableSetMap = std::unordered_map<String, std::unordered_set<String>>;
+    using TableSet = std::set<String>;
+    using DbToTableSetMap = std::map<String, TableSet>;
     const DbToTableSetMap & getSourceDatabasesAndTables(ContextPtr context) const;
     ColumnsDescription getActualTableStructure(ContextPtr context) const override;
     void parseArguments(const ASTPtr & ast_function, ContextPtr context) override;
-    static NameSet getMatchedTablesWithAccess(const String & database_name, const String & table_regexp, const ContextPtr & context);
+    static TableSet getMatchedTablesWithAccess(const String & database_name, const String & table_regexp, const ContextPtr & context);
 
     String source_database_name_or_regexp;
     String source_table_regexp;
diff --git a/tests/queries/0_stateless/00717_merge_and_distributed.reference b/tests/queries/0_stateless/00717_merge_and_distributed.reference
index ec6c2725a2a..073df56d693 100644
--- a/tests/queries/0_stateless/00717_merge_and_distributed.reference
+++ b/tests/queries/0_stateless/00717_merge_and_distributed.reference
@@ -49,9 +49,9 @@
 2018-08-01	100
 2018-08-01	200
 --------------Implicit type conversion------------
+2018-08-01	-1
+2018-08-01	1
+2018-08-01	-1
 2018-08-01	1
-2018-08-01	18446744073709551615
-2018-08-01	1
-2018-08-01	18446744073709551615
 2018-08-01	1
 2018-08-01	1