diff --git a/src/automata.cpp b/src/automata.cpp
index 7896118..57a08e5 100644
--- a/src/automata.cpp
+++ b/src/automata.cpp
@@ -1,5 +1,6 @@
 #include "Lexesis/automata.h"
 
+#include <cassert>
 #include <algorithm>
 #include <climits>
 #include <queue>
@@ -103,8 +104,9 @@ namespace lxs {
         while(!statequeue.empty()) {
             auto state = statequeue.front();
             statequeue.pop();
-            const auto& newStates = epsilonTransitions.find(state)->second;
-            for(auto newstate: newStates) {
+            const auto newStatesIt = epsilonTransitions.find(state);
+            if (newStatesIt == epsilonTransitions.end()) continue;
+            for(const auto& newstate: newStatesIt->second) {
                 if(states.find(newstate) == states.end()) {
                     states.insert(newstate);
                     statequeue.push(newstate);