diff --git a/backends/aiger/xaiger.cc b/backends/aiger/xaiger.cc
index 5d125b653..c69b0fa85 100644
--- a/backends/aiger/xaiger.cc
+++ b/backends/aiger/xaiger.cc
@@ -542,18 +542,30 @@ struct XAigerWriter
 		}
 
 		for (auto bit : unused_bits)
-			undriven_bits.erase(bit);
+			if (holes_mode)
+				undriven_bits.erase(bit);
+			else if (!undriven_bits.count(bit))
+				output_bits.insert(bit);
 
-		if (!undriven_bits.empty() && !holes_mode) {
-			bool whole_module = module->design->selected_whole_module(module->name);
-			undriven_bits.sort();
-			for (auto bit : undriven_bits) {
-				if (whole_module)
-					log_warning("Treating undriven bit %s.%s like $anyseq.\n", log_id(module), log_signal(bit));
-				input_bits.insert(bit);
+		if (!holes_mode) {
+			for (auto port : module->ports) {
+				auto wire = module->wire(port);
+				if (!wire->port_output)
+					continue;
+				for (int i = 0; i < GetSize(wire); i++) {
+					SigBit wirebit(wire, i);
+					SigBit bit = sigmap(wirebit);
+					if (bit == State::Sx)
+						continue;
+					if (!undriven_bits.count(bit)) {
+						output_bits.insert(wirebit);
+					}
+				}
 			}
-			if (whole_module)
-				log_warning("Treating a total of %d undriven bits in %s like $anyseq.\n", GetSize(undriven_bits), log_id(module));
+
+			if (!undriven_bits.empty())
+				for (auto bit : undriven_bits)
+					input_bits.insert(bit);
 		}
 
 		if (holes_mode) {