diff --git a/rstan/rstan/src/misc.cpp b/rstan/rstan/src/misc.cpp
index 5aa821726..5f2b1904a 100644
--- a/rstan/rstan/src/misc.cpp
+++ b/rstan/rstan/src/misc.cpp
@@ -44,10 +44,8 @@ SEXP is_Null_NS(SEXP ns) {
   LOGICAL(ans)[0] = 1;
   PROTECT(ns);
   if (TYPEOF(ns) == EXTPTRSXP) {
-    // Rprintf("ptr=%p.\n", EXTPTR_PTR(ns));
-    if (EXTPTR_PTR(ns) != NULL) LOGICAL(ans)[0] = 0;
+    if (R_ExternalPtrAddr(ns) != NULL) LOGICAL(ans)[0] = 0;
   }
   UNPROTECT(2);
   return ans;
 }
-