diff --git a/nfa.go b/nfa.go
index 4e7cba3..233a5cb 100644
--- a/nfa.go
+++ b/nfa.go
@@ -55,7 +55,7 @@ func verifyLastStates(start []*State) {
 
 func concatenate(s1 *State, s2 *State) *State {
 	for i := range s1.output {
-		s1.output[i].transitions[s2.content] = unique_append(s1.output[i].transitions[s2.content], s2)
+		s1.output[i].transitions[s2.content], _ = unique_append(s1.output[i].transitions[s2.content], s2)
 	}
 	s1.output = s2.output
 	return s1
@@ -69,9 +69,9 @@ func kleene(s1 State) *State {
 	toReturn.isKleene = true
 	toReturn.output = append(toReturn.output, toReturn)
 	for i := range s1.output {
-		s1.output[i].transitions[toReturn.content] = unique_append(s1.output[i].transitions[toReturn.content], toReturn)
+		s1.output[i].transitions[toReturn.content], _ = unique_append(s1.output[i].transitions[toReturn.content], toReturn)
 	}
-	toReturn.transitions[s1.content] = unique_append(toReturn.transitions[s1.content], &s1)
+	toReturn.transitions[s1.content], _ = unique_append(toReturn.transitions[s1.content], &s1)
 	return toReturn
 }
 
@@ -85,8 +85,8 @@ func alternate(s1 *State, s2 *State) *State {
 	// For example, given the transition 'a', the state 's1' can only be mentioned once.
 	// This would lead to multiple instances of the same set of match indices, since both
 	// 's1' states would be considered to match.
-	toReturn.transitions[s1.content] = unique_append(toReturn.transitions[s1.content], s1)
-	toReturn.transitions[s2.content] = unique_append(toReturn.transitions[s2.content], s2)
+	toReturn.transitions[s1.content], _ = unique_append(toReturn.transitions[s1.content], s1)
+	toReturn.transitions[s2.content], _ = unique_append(toReturn.transitions[s2.content], s2)
 	toReturn.content = EPSILON
 	toReturn.isEmpty = true