diff --git a/passes/sat/sim.cc b/passes/sat/sim.cc
index 2f353672b..325e12320 100644
--- a/passes/sat/sim.cc
+++ b/passes/sat/sim.cc
@@ -188,6 +188,10 @@ struct SimInstance
 	{
 		log_assert(module);
 
+		if (module->get_blackbox_attribute(true))
+			log_error("Cannot simulate blackbox module %s (instanced at %s).\n",
+					  log_id(module->name), hiername().c_str());
+
 		if (parent) {
 			log_assert(parent->children.count(instance) == 0);
 			parent->children[instance] = this;