diff --git a/src/Storages/StoragePostgreSQL.cpp b/src/Storages/StoragePostgreSQL.cpp
index 78d3351e2f0..2cc2a15e573 100644
--- a/src/Storages/StoragePostgreSQL.cpp
+++ b/src/Storages/StoragePostgreSQL.cpp
@@ -212,6 +212,7 @@ public:
         data_type->serializeAsText(*array_column, 0, ostr, FormatSettings{});
 
         /// ostr is guaranteed to be at least '[]', i.e. size is at least 2 and 2 only if ostr.str() == '[]'
+        assert(ostr.str().size() >= 2);
         return '{' + std::string(ostr.str().begin() + 1, ostr.str().end() - 1) + '}';
     }