diff --git a/src/core/expr/fexpr.cc b/src/core/expr/fexpr.cc
index 8b6458c9b..8d5f95f46 100644
--- a/src/core/expr/fexpr.cc
+++ b/src/core/expr/fexpr.cc
@@ -533,7 +533,8 @@ DECLARE_METHOD(&PyFExpr::min)
 
 oobj PyFExpr::nth(const XArgs& args) {
   auto nthFn = oobj::import("datatable", "nth");
-  auto n = args[1].to<py::oobj>(py::oint(0));
+  oobj n = args[0].to_oobj() ? args[0].to_oobj() 
+                             : py::oint(0);
   oobj skipna = args[1].to_oobj_or_none();
   return nthFn.call({this, n, skipna});
 }