diff --git a/plugins/fr.irisa.atsyra.absystem.model/src/fr/irisa/atsyra/absystem/model/absystem/util/ABSSizeInfo.java b/plugins/fr.irisa.atsyra.absystem.model/src/fr/irisa/atsyra/absystem/model/absystem/util/ABSSizeInfo.java
index 6c204bc7acc95556d0092bac3ee587ea4a123aa2..8ea8f3be1ec3f7d6071e0429bb272a86a5568c88 100644
--- a/plugins/fr.irisa.atsyra.absystem.model/src/fr/irisa/atsyra/absystem/model/absystem/util/ABSSizeInfo.java
+++ b/plugins/fr.irisa.atsyra.absystem.model/src/fr/irisa/atsyra/absystem/model/absystem/util/ABSSizeInfo.java
@@ -103,7 +103,7 @@ public class ABSSizeInfo {
 				for (GuardedAction guardedAction : dg.getGuardedActions()) {
 					int nbInstances = 1;
 					for(GuardParameter param : guardedAction.getGuardParameters()) {
-						nbInstances *= assetInstanceCount.get(param.getParameterType());
+						nbInstances *= assetInstanceCount.getOrDefault(param.getParameterType(),0);
 					}
 					nbGuardedActionInstance += nbInstances;
 				}