diff --git a/src/EnvironmentWatcher.cpp b/src/EnvironmentWatcher.cpp
index 2daae2f..d58e238 100644
--- a/src/EnvironmentWatcher.cpp
+++ b/src/EnvironmentWatcher.cpp
@@ -484,10 +484,10 @@ RC2::EnvironmentWatcher::setDimNames ( RObject& robj, json& jobj )
 		jobj["dims"] = rvectorToJsonArray(robj);
 	}
 	if (robj.hasAttribute("dimnames")) {
-		RObject mlist(robj.attr("dimnames"));
+		Rcpp::List mlist(robj.attr("dimnames"));
 		json dnames;
-		for (int i=0; i < LENGTH(mlist); i++) {
-			RObject cl(VECTOR_ELT(mlist, i));
+		for (int i=0; i < mlist.length(); i++) {
+			RObject cl(mlist[i]);
 			dnames.push_back(rvectorToJsonArray(cl));
 		}
 		jobj["dimnames"] = dnames;