diff --git a/src/lib/runOscillator.ts b/src/lib/runOscillator.ts
index 3c1ff6a..b06b864 100644
--- a/src/lib/runOscillator.ts
+++ b/src/lib/runOscillator.ts
@@ -16,6 +16,12 @@ export type RunOscillatorResult = {
   world: WorldWithHistory;
 };
 
+export class MaxGenerationError extends Error {
+  constructor(maxGen: number) {
+    super("Maximum generation is " + maxGen);
+  }
+}
+
 export function runOscillator(
   config: RunOscillatorConfig
 ): RunOscillatorResult {
@@ -28,7 +34,7 @@ export function runOscillator(
         forceStop: () => world.getGen() >= maxGeneration,
       });
       if (result === "forced-stop") {
-        throw new Error("Max Generations.");
+        throw new MaxGenerationError(config.maxGeneration);
       }
       return {
         world,
diff --git a/src/worker.ts b/src/worker.ts
index 45f2ecc..394b3b4 100644
--- a/src/worker.ts
+++ b/src/worker.ts
@@ -1,6 +1,7 @@
 import { analyzeOscillator, type AnalyzeResult } from "./lib/analyzeOscillator";
 import { parseRLE } from "@ca-ts/rle";
 import { parseRule } from "@ca-ts/rule";
+import { MaxGenerationError } from "./lib/runOscillator";
 
 export type WorkerRequestMessage = {
   kind: "request-analyze";
@@ -56,7 +57,7 @@ function handleRequest(data: WorkerRequestMessage): WorkerResponseMessage {
       message: "Empty pattern",
     };
   }
-
+  const maxGeneration = rule.type === "int" ? 2_000 : 50_000;
   try {
     const result = analyzeOscillator({
       cells: cells,
@@ -64,11 +65,17 @@ function handleRequest(data: WorkerRequestMessage): WorkerResponseMessage {
         rule.type === "int"
           ? { intTransition: rule.transition }
           : { transition: rule.transition },
-      maxGeneration: rule.type === "int" ? 2_000 : 50_000,
+      maxGeneration: maxGeneration,
     });
     return { kind: "response-analyzed", data: result };
   } catch (error) {
     console.error(error);
+    if (error instanceof MaxGenerationError) {
+      return {
+        kind: "response-error",
+        message: `maximum period is ${maxGeneration.toLocaleString()}`,
+      };
+    }
     return {
       kind: "response-error",
       message: "Analyzation Error",