diff --git a/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/internal/DisproverCommand.java b/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/internal/DisproverCommand.java
index 4ca492fab3ae241465a781ba51ee4f0c27005a97..f8b87c05c86ac015ffe1f4a770244bb7e3c0c53a 100644
--- a/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/internal/DisproverCommand.java
+++ b/de.prob.eventb.disprover.core/src/de/prob/eventb/disprover/core/internal/DisproverCommand.java
@@ -107,7 +107,7 @@ public class DisproverCommand implements IComposableCommand {
 		job.schedule();
 
 		while (job.getResult() == null && 
-		       (pm==null or !pm.isCanceled())) {
+		       (pm==null or !pm.isCanceled())) { // try to treat case IProofMonitor pm is null
 			Thread.sleep(200);
 		}