diff --git a/lib/simulator.js b/lib/simulator.js
index 1cc6195..8377332 100644
--- a/lib/simulator.js
+++ b/lib/simulator.js
@@ -23,8 +23,9 @@
 	var rt = sim.assocs.relevantTerms()
 	if (sim.excludeAncestralTerms || sim.termAssociationCutoff)
 	  rt = rt.filter (function (termIndex) {
-	    return ontology.children[termIndex].length == 0
-	      && (typeof(sim.termAssociationCutoff) === 'undefined'
+	    return (!sim.excludeAncestralTerms
+		    || ontology.children[termIndex].length == 0)
+	      && (!sim.termAssociationCutoff
 		  || sim.assocs.genesByTerm[termIndex].length < sim.termAssociationCutoff)
 	  })
 	for (var i = 0; i < rt.length - 1; ++i) {  // Fisher-Yates shuffle