diff --git a/sqlmodel/sql/sqltypes.py b/sqlmodel/sql/sqltypes.py
index 512daacbab..e8e3fc6bc1 100644
--- a/sqlmodel/sql/sqltypes.py
+++ b/sqlmodel/sql/sqltypes.py
@@ -11,6 +11,6 @@ class AutoString(types.TypeDecorator):  # type: ignore
 
     def load_dialect_impl(self, dialect: Dialect) -> "types.TypeEngine[Any]":
         impl = cast(types.String, self.impl)
-        if impl.length is None and dialect.name == "mysql":
+        if impl.length is None and dialect.name in ("mysql", "mariadb"):
             return dialect.type_descriptor(types.String(self.mysql_default_length))
         return super().load_dialect_impl(dialect)