diff --git a/backends/aiger/aiger.cc b/backends/aiger/aiger.cc
index 4fb47f0d6..2815abda8 100644
--- a/backends/aiger/aiger.cc
+++ b/backends/aiger/aiger.cc
@@ -89,7 +89,7 @@ struct AigerWriter
 				aig_map[bit] = mkgate(a0, a1);
 			} else
 			if (alias_map.count(bit)) {
-                int a = bit2aig(alias_map.at(bit));
+				int a = bit2aig(alias_map.at(bit));
 				aig_map[bit] = a;
 			}