diff --git a/packages/ide/test/fs.test.ts b/packages/ide/test/fs.test.ts
index 856ae476..e49afab6 100644
--- a/packages/ide/test/fs.test.ts
+++ b/packages/ide/test/fs.test.ts
@@ -496,8 +496,9 @@ describe("fs", () => {
 		});
 
 		it("should fail to stat nonexistent file", async () => {
-			await expect(util.promisify(fs.stat)(tmpFile()))
-				.rejects.toThrow("ENOENT");
+			const error = await util.promisify(fs.stat)(tmpFile()).catch((e) => e);
+			expect(error.message).toContain("ENOENT");
+			expect(error.code).toBe("ENOENT");
 		});
 	});
 
diff --git a/packages/protocol/src/browser/client.ts b/packages/protocol/src/browser/client.ts
index 0e0960bd..b20dea23 100644
--- a/packages/protocol/src/browser/client.ts
+++ b/packages/protocol/src/browser/client.ts
@@ -98,7 +98,7 @@ export class Client {
 				const eventsMsg = new EvalEventMessage();
 				eventsMsg.setId(doEval.id);
 				eventsMsg.setEvent(event);
-				eventsMsg.setArgsList(args.map(stringify));
+				eventsMsg.setArgsList(args.map((a) => stringify(a)));
 				const clientMsg = new ClientMessage();
 				clientMsg.setEvalEvent(eventsMsg);
 				this.connection.send(clientMsg.serializeBinary());
@@ -140,7 +140,7 @@ export class Client {
 		const id = this.evalId++;
 		newEval.setId(id);
 		newEval.setActive(active);
-		newEval.setArgsList([a1, a2, a3, a4, a5, a6].map(stringify));
+		newEval.setArgsList([a1, a2, a3, a4, a5, a6].map((a) => stringify(a)));
 		newEval.setFunction(func.toString());
 
 		const clientMsg = new ClientMessage();
@@ -155,16 +155,15 @@ export class Client {
 
 			const d1 = this.evalDoneEmitter.event((doneMsg) => {
 				if (doneMsg.getId() === id) {
-					const resp = doneMsg.getResponse();
 					dispose();
-					resolve(parse(resp));
+					resolve(parse(doneMsg.getResponse()));
 				}
 			});
 
 			const d2 = this.evalFailedEmitter.event((failedMsg) => {
 				if (failedMsg.getId() === id) {
 					dispose();
-					reject(new Error(failedMsg.getMessage()));
+					reject(parse(failedMsg.getResponse()));
 				}
 			});
 		});
diff --git a/packages/protocol/src/common/util.ts b/packages/protocol/src/common/util.ts
index bc96ba9c..9a2998b6 100644
--- a/packages/protocol/src/common/util.ts
+++ b/packages/protocol/src/common/util.ts
@@ -25,17 +25,19 @@ export type IEncodingOptions = {
 export type IEncodingOptionsCallback = IEncodingOptions | ((err: NodeJS.ErrnoException, ...args: any[]) => void);
 
 /**
- * Stringify an event argument.
+ * Stringify an event argument. isError is because although methods like
+ * `fs.stat` are supposed to throw Error objects, they currently throw regular
+ * objects when running tests through Jest.
  */
-export const stringify = (arg: any): string => { // tslint:disable-line no-any
-	if (arg instanceof Error) {
+export const stringify = (arg: any, isError?: boolean): string => { // tslint:disable-line no-any
+	if (arg instanceof Error || isError) {
 		// Errors don't stringify at all. They just become "{}".
 		return JSON.stringify({
 			type: "Error",
 			data: {
 				message: arg.message,
-				name: arg.name,
 				stack: arg.stack,
+				code: (arg as NodeJS.ErrnoException).code,
 			},
 		});
 	} else if (arg instanceof Uint8Array) {
@@ -74,7 +76,16 @@ export const parse = (arg: string): any => { // tslint:disable-line no-any
 			// what happens to buffers and stringify them as regular objects.
 			case "Error":
 				if (result.data.message) {
-					return new Error(result.data.message);
+					const error = new Error(result.data.message);
+					// TODO: Can we set the stack? Doing so seems to make it into an
+					// "invalid object".
+					if (typeof result.data.code !== "undefined") {
+						(error as NodeJS.ErrnoException).code = result.data.code;
+					}
+					// tslint:disable-next-line no-any
+					(error as any).originalStack = result.data.stack;
+
+					return error;
 				}
 				break;
 		}
diff --git a/packages/protocol/src/node/evaluate.ts b/packages/protocol/src/node/evaluate.ts
index 3d66ccd9..58f07baf 100644
--- a/packages/protocol/src/node/evaluate.ts
+++ b/packages/protocol/src/node/evaluate.ts
@@ -36,8 +36,7 @@ export const evaluate = (connection: SendableConnection, message: NewEvalMessage
 	const sendException = (error: Error): void => {
 		const evalFailed = new EvalFailedMessage();
 		evalFailed.setId(message.getId());
-		evalFailed.setReason(EvalFailedMessage.Reason.EXCEPTION);
-		evalFailed.setMessage(error.toString() + " " + error.stack);
+		evalFailed.setResponse(stringify(error, true));
 
 		const serverMsg = new ServerMessage();
 		serverMsg.setEvalFailed(evalFailed);
@@ -58,7 +57,7 @@ export const evaluate = (connection: SendableConnection, message: NewEvalMessage
 					logger.trace(() => [
 						`${event}`,
 						field("id", message.getId()),
-						field("args", args.map(stringify)),
+						field("args", args.map((a) => stringify(a))),
 					]);
 					cb(...args);
 				});
@@ -67,11 +66,11 @@ export const evaluate = (connection: SendableConnection, message: NewEvalMessage
 				logger.trace(() => [
 					`emit ${event}`,
 					field("id", message.getId()),
-					field("args", args.map(stringify)),
+					field("args", args.map((a) => stringify(a))),
 				]);
 				const eventMsg = new EvalEventMessage();
 				eventMsg.setEvent(event);
-				eventMsg.setArgsList(args.map(stringify));
+				eventMsg.setArgsList(args.map((a) => stringify(a)));
 				eventMsg.setId(message.getId());
 				const serverMsg = new ServerMessage();
 				serverMsg.setEvalEvent(eventMsg);
diff --git a/packages/protocol/src/proto/node.proto b/packages/protocol/src/proto/node.proto
index 7af94bec..e71a04f0 100644
--- a/packages/protocol/src/proto/node.proto
+++ b/packages/protocol/src/proto/node.proto
@@ -19,13 +19,7 @@ message EvalEventMessage {
 
 message EvalFailedMessage {
 	uint64 id = 1;
-	enum Reason {
-		Timeout = 0;
-		Exception = 1;
-		Conflict = 2;
-	}
-	Reason reason = 2;
-	string message = 3;
+	string response = 2;
 }
 
 message EvalDoneMessage {
diff --git a/packages/protocol/src/proto/node_pb.d.ts b/packages/protocol/src/proto/node_pb.d.ts
index 3edcd235..1b36e86b 100644
--- a/packages/protocol/src/proto/node_pb.d.ts
+++ b/packages/protocol/src/proto/node_pb.d.ts
@@ -75,11 +75,8 @@ export class EvalFailedMessage extends jspb.Message {
   getId(): number;
   setId(value: number): void;
 
-  getReason(): EvalFailedMessage.Reason;
-  setReason(value: EvalFailedMessage.Reason): void;
-
-  getMessage(): string;
-  setMessage(value: string): void;
+  getResponse(): string;
+  setResponse(value: string): void;
 
   serializeBinary(): Uint8Array;
   toObject(includeInstance?: boolean): EvalFailedMessage.AsObject;
@@ -94,14 +91,7 @@ export class EvalFailedMessage extends jspb.Message {
 export namespace EvalFailedMessage {
   export type AsObject = {
     id: number,
-    reason: EvalFailedMessage.Reason,
-    message: string,
-  }
-
-  export enum Reason {
-    TIMEOUT = 0,
-    EXCEPTION = 1,
-    CONFLICT = 2,
+    response: string,
   }
 }
 
diff --git a/packages/protocol/src/proto/node_pb.js b/packages/protocol/src/proto/node_pb.js
index ce4ccbe6..289eb9a9 100644
--- a/packages/protocol/src/proto/node_pb.js
+++ b/packages/protocol/src/proto/node_pb.js
@@ -14,7 +14,6 @@ var global = Function('return this')();
 goog.exportSymbol('proto.EvalDoneMessage', null, global);
 goog.exportSymbol('proto.EvalEventMessage', null, global);
 goog.exportSymbol('proto.EvalFailedMessage', null, global);
-goog.exportSymbol('proto.EvalFailedMessage.Reason', null, global);
 goog.exportSymbol('proto.NewEvalMessage', null, global);
 
 /**
@@ -554,8 +553,7 @@ proto.EvalFailedMessage.prototype.toObject = function(opt_includeInstance) {
 proto.EvalFailedMessage.toObject = function(includeInstance, msg) {
   var f, obj = {
     id: jspb.Message.getFieldWithDefault(msg, 1, 0),
-    reason: jspb.Message.getFieldWithDefault(msg, 2, 0),
-    message: jspb.Message.getFieldWithDefault(msg, 3, "")
+    response: jspb.Message.getFieldWithDefault(msg, 2, "")
   };
 
   if (includeInstance) {
@@ -597,12 +595,8 @@ proto.EvalFailedMessage.deserializeBinaryFromReader = function(msg, reader) {
       msg.setId(value);
       break;
     case 2:
-      var value = /** @type {!proto.EvalFailedMessage.Reason} */ (reader.readEnum());
-      msg.setReason(value);
-      break;
-    case 3:
       var value = /** @type {string} */ (reader.readString());
-      msg.setMessage(value);
+      msg.setResponse(value);
       break;
     default:
       reader.skipField();
@@ -640,32 +634,16 @@ proto.EvalFailedMessage.serializeBinaryToWriter = function(message, writer) {
       f
     );
   }
-  f = message.getReason();
-  if (f !== 0.0) {
-    writer.writeEnum(
+  f = message.getResponse();
+  if (f.length > 0) {
+    writer.writeString(
       2,
       f
     );
   }
-  f = message.getMessage();
-  if (f.length > 0) {
-    writer.writeString(
-      3,
-      f
-    );
-  }
 };
 
 
-/**
- * @enum {number}
- */
-proto.EvalFailedMessage.Reason = {
-  TIMEOUT: 0,
-  EXCEPTION: 1,
-  CONFLICT: 2
-};
-
 /**
  * optional uint64 id = 1;
  * @return {number}
@@ -682,32 +660,17 @@ proto.EvalFailedMessage.prototype.setId = function(value) {
 
 
 /**
- * optional Reason reason = 2;
- * @return {!proto.EvalFailedMessage.Reason}
- */
-proto.EvalFailedMessage.prototype.getReason = function() {
-  return /** @type {!proto.EvalFailedMessage.Reason} */ (jspb.Message.getFieldWithDefault(this, 2, 0));
-};
-
-
-/** @param {!proto.EvalFailedMessage.Reason} value */
-proto.EvalFailedMessage.prototype.setReason = function(value) {
-  jspb.Message.setProto3EnumField(this, 2, value);
-};
-
-
-/**
- * optional string message = 3;
+ * optional string response = 2;
  * @return {string}
  */
-proto.EvalFailedMessage.prototype.getMessage = function() {
-  return /** @type {string} */ (jspb.Message.getFieldWithDefault(this, 3, ""));
+proto.EvalFailedMessage.prototype.getResponse = function() {
+  return /** @type {string} */ (jspb.Message.getFieldWithDefault(this, 2, ""));
 };
 
 
 /** @param {string} value */
-proto.EvalFailedMessage.prototype.setMessage = function(value) {
-  jspb.Message.setProto3StringField(this, 3, value);
+proto.EvalFailedMessage.prototype.setResponse = function(value) {
+  jspb.Message.setProto3StringField(this, 2, value);
 };