diff --git a/backends/aiger/xaiger.cc b/backends/aiger/xaiger.cc
index 99ca4f8d5..7c7697874 100644
--- a/backends/aiger/xaiger.cc
+++ b/backends/aiger/xaiger.cc
@@ -229,9 +229,9 @@ struct XAigerWriter
 							/*if (!output_bits.count(b))*/
 							if (abc_box)
 								co_bits.emplace_back(b, 0);
-							else {
+							else if (b.wire) {
 								output_bits.insert(b);
-								if (b.wire && !b.wire->port_input)
+								if (!b.wire->port_input)
 									unused_bits.erase(b);
 							}
 						}