diff --git a/src/sources/mssql/mssql-schema.lisp b/src/sources/mssql/mssql-schema.lisp
index 666bb66..97d6f9e 100644
--- a/src/sources/mssql/mssql-schema.lisp
+++ b/src/sources/mssql/mssql-schema.lisp
@@ -174,7 +174,7 @@
     (:datetimeoffset (format nil "convert(varchar(35), [~a], 127)" name))
     (:smalldatetime  (format nil "convert(varchar(30), [~a], 126)" name))
     (:date           (format nil "convert(varchar(30), [~a], 126)" name))
-    (:bigint         (format nil "cast([~a] as numeric)" name))
+    (:bigint         (format nil "cast([~a] as numeric(20))" name))
     (t               (format nil "[~a]" name))))
 
 (defmethod get-column-list ((mssql copy-mssql))