diff --git a/backends/aiger/xaiger.cc b/backends/aiger/xaiger.cc
index 8513611..97fec93 100644
--- a/backends/aiger/xaiger.cc
+++ b/backends/aiger/xaiger.cc
@@ -168,7 +168,7 @@
 				}
 
 				if (keep)
-					keep_bits.insert(bit);
+					keep_bits.insert(wirebit);
 
 				if (wire->port_input || keep) {
 					if (bit != wirebit)