diff --git a/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/DisproverReasoner.java b/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/DisproverReasoner.java
index 8921c211d07660d93f00908d14b25c73a7fe7328..1c7f3f8c8ecf5220c35770faf0e2d09d5a775647 100644
--- a/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/DisproverReasoner.java
+++ b/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/DisproverReasoner.java
@@ -133,6 +133,11 @@ public class DisproverReasoner implements IReasoner {
 		Predicate goal = sequent.goal();
 
 		IAntecedent ante = ProverFactory.makeAntecedent(goal);
+		
+		if (counterExample == null) {
+			return ProverFactory.reasonerFailure(this, input,
+					"ProB: Error occurred.");
+		}
 
 		if (counterExample.timeoutOccured()) {
 			System.out.println(sequent.toString() + ": Timeout occured.");