diff --git a/lib/wallet/cryptoApi.ts b/lib/wallet/cryptoApi.ts
index db29592fc..855afbb4e 100644
--- a/lib/wallet/cryptoApi.ts
+++ b/lib/wallet/cryptoApi.ts
@@ -38,11 +38,22 @@ interface WorkerState {
   /**
    * The actual worker thread.
    */
-  w: Worker;
+  w: Worker|null;
+
   /**
    * Are we currently running a task on this worker?
    */
   busy: boolean;
+
+  /**
+   * Timer to terminate the worker if it's not busy enough.
+   */
+  terminationTimerHandle: number|null;
+
+  /**
+   * Index of this worker in the list of workers.
+   */
+  workerIndex: number;
 }
 
 interface WorkItem {
@@ -74,53 +85,99 @@ export class CryptoApi {
   private numWaiting: number = 0;
 
 
-  constructor() {
-    let handler = (msg: MessageEvent) => {
-      let id = msg.data.id;
-      if (typeof id !== "number") {
-        console.error("rpc id must be number");
-        return;
-      }
-      if (!this.rpcRegistry[id]) {
-        console.error(`RPC with id ${id} has no registry entry`);
-        return;
-      }
-      let {resolve, workerIndex} = this.rpcRegistry[id];
-      delete this.rpcRegistry[id];
-      let ws = this.workers[workerIndex];
-      if (!ws.busy) {
-        throw Error("assertion failed");
+  /**
+   * Start a worker (if not started) and set as busy.
+   */
+  wake(ws: WorkerState) {
+    if (ws.busy) {
+      throw Error("assertion failed");
+    }
+    ws.busy = true;
+    this.numBusy++;
+    if (!ws.w) {
+      let w = new Worker("/lib/wallet/cryptoWorker.js");
+      w.onmessage = (m: MessageEvent) => this.handleWorkerMessage(ws, m);
+      w.onerror = (e: ErrorEvent) => this.handleWorkerError(ws, e);
+      ws.w = w;
+    }
+    if (ws.terminationTimerHandle != null) {
+      clearTimeout(ws.terminationTimerHandle);
+    }
+    let destroy = () => {
+      if (ws.w && !ws.busy) {
+        ws.w!.terminate();
+        ws.w = null;
       }
+    }
+    ws.terminationTimerHandle = setTimeout(destroy, 20 * 1000);
+  }
+
+  handleWorkerError(ws: WorkerState, e: ErrorEvent) {
+    console.error("error in worker", e);
+    try {
+      ws.w!.terminate();
+    } catch (e) {
+      console.error(e);
+    }
+    if (ws.busy) {
       ws.busy = false;
       this.numBusy--;
-      resolve(msg.data.result);
+    }
+    this.findWork(ws);
+  }
 
-      // try to find more work for this worker
-      for (let i = 0; i < NUM_PRIO; i++) {
-        let q = this.workQueues[NUM_PRIO - i - 1];
-        if (q.length != 0) {
-          let work: WorkItem = q.shift()!;
-          let msg: any = {
-            operation: work.operation,
-            args: work.args,
-            id: this.registerRpcId(work.resolve, work.reject, workerIndex),
-          };
-          ws.w.postMessage(msg);
-          ws.busy = true;
-          this.numBusy++;
-          return;
-        }
+  findWork(ws: WorkerState) {
+    // try to find more work for this worker
+    for (let i = 0; i < NUM_PRIO; i++) {
+      let q = this.workQueues[NUM_PRIO - i - 1];
+      if (q.length != 0) {
+        let work: WorkItem = q.shift()!;
+        let msg: any = {
+          operation: work.operation,
+          args: work.args,
+          id: this.registerRpcId(work.resolve, work.reject, ws.workerIndex),
+        };
+
+        this.wake(ws);
+        ws.w!.postMessage(msg);
+        return;
       }
-    };
+    }
+  }
 
+  handleWorkerMessage(ws: WorkerState, msg: MessageEvent) {
+    let id = msg.data.id;
+    if (typeof id !== "number") {
+      console.error("rpc id must be number");
+      return;
+    }
+    if (!this.rpcRegistry[id]) {
+      console.error(`RPC with id ${id} has no registry entry`);
+      return;
+    }
+    let {resolve, workerIndex} = this.rpcRegistry[id];
+    delete this.rpcRegistry[id];
+    if (workerIndex != ws.workerIndex) {
+      throw Error("assertion failed");
+    }
+    if (!ws.busy) {
+      throw Error("assertion failed");
+    }
+    ws.busy = false;
+    this.numBusy--;
+    resolve(msg.data.result);
+    this.findWork(ws);
+  }
+
+  constructor() {
     this.workers = new Array<WorkerState>((navigator as any)["hardwareConcurrency"] || 2);
 
     for (let i = 0; i < this.workers.length; i++) {
-      let w = new Worker("/lib/wallet/cryptoWorker.js");
-      w.onmessage = handler;
       this.workers[i] = {
-        w,
+        w: null,
         busy: false,
+        terminationTimerHandle: null,
+        workerIndex: i,
       };
     }
     this.workQueues = [];
@@ -156,15 +213,14 @@ export class CryptoApi {
         continue;
       }
 
-      ws.busy = true;
-      this.numBusy++;
+      this.wake(ws);
 
       return new Promise<T>((resolve, reject) => {
         let msg: any = {
           operation, args,
           id: this.registerRpcId(resolve, reject, i),
         };
-        ws.w.postMessage(msg);
+        ws.w!.postMessage(msg);
       });
     }