diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index cd1507ba0..0ca60a3e4 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -1236,6 +1236,16 @@ struct RTLIL::SigSpecConstIterator
 	inline bool operator==(const RTLIL::SigSpecConstIterator &other) const { return bit_index == other.bit_index; }
 	inline RTLIL::SigSpecConstIterator &operator++();
 	inline RTLIL::SigSpecConstIterator &operator--();
+	inline RTLIL::SigSpecConstIterator operator++(int) {
+		RTLIL::SigSpecConstIterator result(*this);
+		++(*this);
+		return result;
+	}
+	inline RTLIL::SigSpecConstIterator operator--(int) {
+		RTLIL::SigSpecConstIterator result(*this);
+		--(*this);
+		return result;
+	}
 
 private:
 	// Must be called when sig_p is packed and `bit_index` is in range. Finds the chunk containing `bit_index`
diff --git a/kernel/sigtools.h b/kernel/sigtools.h
index 3155d7482..f5798d433 100644
--- a/kernel/sigtools.h
+++ b/kernel/sigtools.h
@@ -72,8 +72,9 @@ struct SigPool
 	void expand(const RTLIL::SigSpec &from, const RTLIL::SigSpec &to)
 	{
 		log_assert(GetSize(from) == GetSize(to));
-		for (int i = 0; i < GetSize(from); i++) {
-			bitDef_t bit_from(from[i]), bit_to(to[i]);
+		RTLIL::SigSpecConstIterator to_it = to.begin();
+		for (auto &bit : from) {
+			bitDef_t bit_from(bit), bit_to(*to_it++);
 			if (bit_from.first != NULL && bit_to.first != NULL && bits.count(bit_from) > 0)
 				bits.insert(bit_to);
 		}
@@ -321,10 +322,11 @@ struct SigMap final : public SigMapView
 	{
 		log_assert(GetSize(from) == GetSize(to));
 
-		for (int i = 0; i < GetSize(from); i++)
+		RTLIL::SigSpecConstIterator to_it = to.begin();
+		for (auto &bit : from)
 		{
-			int bfi = database.lookup(from[i]);
-			int bti = database.lookup(to[i]);
+			int bfi = database.lookup(bit);
+			int bti = database.lookup(*to_it++);
 
 			const RTLIL::SigBit &bf = database[bfi];
 			const RTLIL::SigBit &bt = database[bti];
@@ -415,10 +417,11 @@ struct SigValMap final : public SigMapView
 	{
 		log_assert(GetSize(from) == GetSize(to));
 
-		for (int i = 0; i < GetSize(from); i++)
+		RTLIL::SigSpecConstIterator to_it = to.begin();
+		for (auto &bit : from)
 		{
-			int bfi = database.lookup(from[i]);
-			int bti = database.lookup(to[i]);
+			int bfi = database.lookup(bit);
+			int bti = database.lookup(*to_it++);
 			if (bfi == bti) {
 				continue;
 			}