diff --git a/lib/read_mealy.cpp b/lib/read_mealy.cpp
index f4cc1c48e652346a63154373bcfb320d993a5c02..c19429e4a631aa2583dec7d14d5f335356844c4f 100644
--- a/lib/read_mealy.cpp
+++ b/lib/read_mealy.cpp
@@ -44,7 +44,7 @@ mealy read_mealy_from_txt(std::istream & in) {
 		v.resize(max_input);
 		v[i] = mealy::edge(to, o);
 
-		assert(defined(m, to, i));
+		assert(defined(m, from, i));
 	}
 
 	m.graph_size = max_state;