diff --git a/lib/param-helper.js b/lib/param-helper.js
index 9efbef7..6104578 100644
--- a/lib/param-helper.js
+++ b/lib/param-helper.js
@@ -129,7 +129,7 @@ function baseParams(params) {
   params.mu = constants.MU;
   params.bodyRadius = constants.EARTH_RADIUS;
 
-  return ld.merge(DEFAULT_PARAMS, params);
+  return ld.extend({}, DEFAULT_PARAMS, params);
 }
 
 function angularMomentumFromSemilatusRectum(semilatusRectum) {