diff --git a/src/fsm.js b/src/fsm.js
index 8aae5cd..1fe54bf 100644
--- a/src/fsm.js
+++ b/src/fsm.js
@@ -95,7 +95,9 @@ export function openAutomaton(name, states, editable = false) {
     for (const s of state) {
       if (s in states) {
         const transitions = states[s].transitions[letter];
-        newStates.push(...transitions);
+        if (transitions) {
+          newStates.push(...transitions);
+        }
       }
     }
     state = newStates;