diff --git a/src/data/pack.cpp b/src/data/pack.cpp
index 01074f82..3e8f796d 100644
--- a/src/data/pack.cpp
+++ b/src/data/pack.cpp
@@ -384,6 +384,7 @@ void PackGenerator::reset(int seed) {
 }
 
 PackInstance& PackGenerator::get(const String& name) {
+	assert(set);
 	PackInstanceP& instance = instances[name];
 	if (instance) {
 		return *instance;