diff --git a/kernel/modtools.h b/kernel/modtools.h
index 27ba98d7d..b0446d454 100644
--- a/kernel/modtools.h
+++ b/kernel/modtools.h
@@ -78,6 +78,7 @@ struct ModIndex : public RTLIL::Monitor
 	SigMap sigmap;
 	RTLIL::Module *module;
 	std::map<RTLIL::SigBit, SigBitInfo> database;
+	int reload_counter;
 	int auto_reload_counter;
 	bool auto_reload_module;
 
@@ -106,6 +107,10 @@ struct ModIndex : public RTLIL::Monitor
 
 	void reload_module(bool reset_sigmap = true)
 	{
+		reload_counter++;
+		if (reload_counter % 10 == 0)
+			log_warning("ModIndex::reload_module() called %d times.\n", reload_counter);
+
 		if (reset_sigmap) {
 			sigmap.clear();
 			sigmap.set(module);
@@ -231,6 +236,7 @@ struct ModIndex : public RTLIL::Monitor
 
 	ModIndex(RTLIL::Module *_m) : sigmap(_m), module(_m)
 	{
+		reload_counter = 0;
 		auto_reload_counter = 0;
 		auto_reload_module = true;
 		module->monitors.insert(this);
diff --git a/passes/opt/wreduce.cc b/passes/opt/wreduce.cc
index 9e710d525..187b296a6 100644
--- a/passes/opt/wreduce.cc
+++ b/passes/opt/wreduce.cc
@@ -78,6 +78,8 @@ struct WreduceWorker
 		for (int i = GetSize(sig_y)-1; i >= 0; i--)
 		{
 			auto info = mi.query(sig_y[i]);
+			if (info == nullptr)
+				return;
 			if (!info->is_output && GetSize(info->ports) <= 1 && !keep_bits.count(mi.sigmap(sig_y[i]))) {
 				bits_removed.push_back(State::Sx);
 				continue;
@@ -408,6 +410,8 @@ struct WreduceWorker
 					break;
 
 				auto info = mi.query(bit);
+				if (info == nullptr)
+					return;
 				if (info->is_output || GetSize(info->ports) > 1)
 					break;
 
@@ -566,6 +570,10 @@ struct WreduceWorker
 			for (int i = GetSize(w)-1; i >= 0; i--) {
 				SigBit bit(w, i);
 				auto info = mi.query(bit);
+				if (info == nullptr) {
+					unused_top_bits = 0;
+					break;
+				}
 				if (info && (info->is_input || info->is_output || GetSize(info->ports) > 0))
 					break;
 				unused_top_bits++;