diff --git a/src/sim/world.js b/src/sim/world.js
index 95f457c..85d041f 100644
--- a/src/sim/world.js
+++ b/src/sim/world.js
@@ -82,10 +82,15 @@ const HANDLERS = {
 
 // Advance the world to absolute time toTime, processing all due events in order.
 export function advance(world, toTime) {
-  while (world.queue.size > 0 && world.queue.peek().time <= toTime) {
-    const ev = world.queue.pop();
-    world.t = ev.time;
-    HANDLERS[ev.type](world, ev.data);
+  try {
+    while (world.queue.size > 0 && world.queue.peek().time <= toTime) {
+      const ev = world.queue.pop();
+      world.t = ev.time;
+      const handler = HANDLERS[ev.type];
+      if (!handler) throw new Error(`Unknown event type: ${ev.type}`);
+      handler(world, ev.data);
+    }
+  } finally {
+    world.t = toTime;
   }
-  world.t = toTime;
 }