diff --git a/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/internal/DisproverReasoner.java b/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/internal/DisproverReasoner.java
index d8a105cccab1ed6e7956eb55fa3b9716ef904ce1..2f935d439d8ff67c1e013cbfb2b868cd67df9abc 100644
--- a/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/internal/DisproverReasoner.java
+++ b/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/internal/DisproverReasoner.java
@@ -133,6 +133,11 @@ public class DisproverReasoner implements IReasoner {
 
 		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.");
 			return ProverFactory.reasonerFailure(this, input,