diff --git a/lib/mapObjectConstructors/CommonConstructors.cpp b/lib/mapObjectConstructors/CommonConstructors.cpp
index 13f286cbf..6a558b96a 100644
--- a/lib/mapObjectConstructors/CommonConstructors.cpp
+++ b/lib/mapObjectConstructors/CommonConstructors.cpp
@@ -133,7 +133,7 @@ void CHeroInstanceConstructor::afterLoadFinalization()
 	{
 		filters[entry.first] = LogicalExpression<HeroTypeID>(entry.second, [](const JsonNode & node)
 		{
-			return HeroTypeID(VLC->identifiers()->getIdentifier("hero", node.Vector()[0]).value());
+			return HeroTypeID(VLC->identifiers()->getIdentifier("hero", node.Vector()[0]).value_or(-1));
 		});
 	}
 }
diff --git a/lib/spells/effects/Summon.cpp b/lib/spells/effects/Summon.cpp
index ac3c0206b..39b4dceca 100644
--- a/lib/spells/effects/Summon.cpp
+++ b/lib/spells/effects/Summon.cpp
@@ -42,6 +42,12 @@ void Summon::adjustTargetTypes(std::vector<TargetType> & types) const
 
 bool Summon::applicable(Problem & problem, const Mechanics * m) const
 {
+	if (creature == CreatureID::NONE)
+	{
+		logMod->error("Attempt to summon non-existing creature!");
+		return m->adaptGenericProblem(problem);
+	}
+
 	if(exclusive)
 	{
 		//check if there are summoned creatures of other type