diff --git a/Sources/AWSLambdaRuntime/LambdaRuntimeClient.swift b/Sources/AWSLambdaRuntime/LambdaRuntimeClient.swift
index 97d64b42..d7b8b69a 100644
--- a/Sources/AWSLambdaRuntime/LambdaRuntimeClient.swift
+++ b/Sources/AWSLambdaRuntime/LambdaRuntimeClient.swift
@@ -12,7 +12,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-import class Foundation.JSONEncoder
 import Logging
 import NIO
 import NIOHTTP1
@@ -68,14 +67,10 @@ extension Lambda {
                 body = buffer
             case .failure(let error):
                 url += Consts.postErrorURLSuffix
-                let error = ErrorResponse(errorType: Consts.functionError, errorMessage: "\(error)")
-                switch error.toJson() {
-                case .failure(let jsonError):
-                    return self.eventLoop.makeFailedFuture(RuntimeError.json(jsonError))
-                case .success(let json):
-                    body = self.allocator.buffer(capacity: json.utf8.count)
-                    body!.writeString(json)
-                }
+                let errorResponse = ErrorResponse(errorType: Consts.functionError, errorMessage: "\(error)")
+                let bytes = errorResponse.toJSONBytes()
+                body = self.allocator.buffer(capacity: bytes.count)
+                body!.writeBytes(bytes)
             }
             logger.debug("reporting results to lambda runtime engine using \(url)")
             return self.httpClient.post(url: url, body: body).flatMapThrowing { response in
@@ -99,28 +94,23 @@ extension Lambda {
         func reportInitializationError(logger: Logger, error: Error) -> EventLoopFuture<Void> {
             let url = Consts.postInitErrorURL
             let errorResponse = ErrorResponse(errorType: Consts.initializationError, errorMessage: "\(error)")
-            var body: ByteBuffer
-            switch errorResponse.toJson() {
-            case .failure(let jsonError):
-                return self.eventLoop.makeFailedFuture(RuntimeError.json(jsonError))
-            case .success(let json):
-                body = self.allocator.buffer(capacity: json.utf8.count)
-                body.writeString(json)
-                logger.warning("reporting initialization error to lambda runtime engine using \(url)")
-                return self.httpClient.post(url: url, body: body).flatMapThrowing { response in
-                    guard response.status == .accepted else {
-                        throw RuntimeError.badStatusCode(response.status)
-                    }
-                    return ()
-                }.flatMapErrorThrowing { error in
-                    switch error {
-                    case HTTPClient.Errors.timeout:
-                        throw RuntimeError.upstreamError("timeout")
-                    case HTTPClient.Errors.connectionResetByPeer:
-                        throw RuntimeError.upstreamError("connectionResetByPeer")
-                    default:
-                        throw error
-                    }
+            let bytes = errorResponse.toJSONBytes()
+            var body = self.allocator.buffer(capacity: bytes.count)
+            body.writeBytes(bytes)
+            logger.warning("reporting initialization error to lambda runtime engine using \(url)")
+            return self.httpClient.post(url: url, body: body).flatMapThrowing { response in
+                guard response.status == .accepted else {
+                    throw RuntimeError.badStatusCode(response.status)
+                }
+                return ()
+            }.flatMapErrorThrowing { error in
+                switch error {
+                case HTTPClient.Errors.timeout:
+                    throw RuntimeError.upstreamError("timeout")
+                case HTTPClient.Errors.connectionResetByPeer:
+                    throw RuntimeError.upstreamError("connectionResetByPeer")
+                default:
+                    throw error
                 }
             }
         }
@@ -142,15 +132,16 @@ internal struct ErrorResponse: Codable {
     var errorMessage: String
 }
 
-private extension ErrorResponse {
-    func toJson() -> Result<String, Error> {
-        let encoder = JSONEncoder()
-        do {
-            let data = try encoder.encode(self)
-            return .success(String(data: data, encoding: .utf8) ?? "unknown error")
-        } catch {
-            return .failure(error)
-        }
+internal extension ErrorResponse {
+    func toJSONBytes() -> [UInt8] {
+        var bytes = [UInt8]()
+        bytes.append(UInt8(ascii: "{"))
+        bytes.append(contentsOf: #""errorType":"# .utf8)
+        self.errorType.encodeAsJSONString(into: &bytes)
+        bytes.append(contentsOf: #","errorMessage":"# .utf8)
+        self.errorMessage.encodeAsJSONString(into: &bytes)
+        bytes.append(UInt8(ascii: "}"))
+        return bytes
     }
 }
 
diff --git a/Sources/AWSLambdaRuntime/Utils.swift b/Sources/AWSLambdaRuntime/Utils.swift
index 929fea77..d31c7ca5 100644
--- a/Sources/AWSLambdaRuntime/Utils.swift
+++ b/Sources/AWSLambdaRuntime/Utils.swift
@@ -78,3 +78,37 @@ internal extension DispatchWallTime {
         Int64(bitPattern: self.rawValue) / -1_000_000
     }
 }
+
+extension String {
+    func encodeAsJSONString(into bytes: inout [UInt8]) {
+        bytes.append(UInt8(ascii: "\""))
+        let stringBytes = self.utf8
+        var startCopyIndex = stringBytes.startIndex
+        var nextIndex = startCopyIndex
+
+        while nextIndex != stringBytes.endIndex {
+            switch stringBytes[nextIndex] {
+            case 0 ..< 32, UInt8(ascii: "\""), UInt8(ascii: "\\"):
+                // All Unicode characters may be placed within the
+                // quotation marks, except for the characters that MUST be escaped:
+                // quotation mark, reverse solidus, and the control characters (U+0000
+                // through U+001F).
+                // https://tools.ietf.org/html/rfc7159#section-7
+
+                // copy the current range over
+                bytes.append(contentsOf: stringBytes[startCopyIndex ..< nextIndex])
+                bytes.append(UInt8(ascii: "\\"))
+                bytes.append(stringBytes[nextIndex])
+
+                nextIndex = stringBytes.index(after: nextIndex)
+                startCopyIndex = nextIndex
+            default:
+                nextIndex = stringBytes.index(after: nextIndex)
+            }
+        }
+
+        // copy everything, that hasn't been copied yet
+        bytes.append(contentsOf: stringBytes[startCopyIndex ..< nextIndex])
+        bytes.append(UInt8(ascii: "\""))
+    }
+}
diff --git a/Tests/AWSLambdaRuntimeTests/LambdaRuntimeClientTest.swift b/Tests/AWSLambdaRuntimeTests/LambdaRuntimeClientTest.swift
index 88a1f1d9..56bd5280 100644
--- a/Tests/AWSLambdaRuntimeTests/LambdaRuntimeClientTest.swift
+++ b/Tests/AWSLambdaRuntimeTests/LambdaRuntimeClientTest.swift
@@ -191,6 +191,24 @@ class LambdaRuntimeClientTest: XCTestCase {
         }
     }
 
+    func testErrorResponseToJSON() {
+        // we want to check if quotes and back slashes are correctly escaped
+        let windowsError = ErrorResponse(
+            errorType: "error",
+            errorMessage: #"underlyingError: "An error with a windows path C:\Windows\""#
+        )
+        let windowsBytes = windowsError.toJSONBytes()
+        XCTAssertEqual(#"{"errorType":"error","errorMessage":"underlyingError: \"An error with a windows path C:\\Windows\\\""}"#, String(decoding: windowsBytes, as: Unicode.UTF8.self))
+
+        // we want to check if unicode sequences work
+        let emojiError = ErrorResponse(
+            errorType: "error",
+            errorMessage: #"🥑👨‍👩‍👧‍👧👩‍👩‍👧‍👧👨‍👨‍👧"#
+        )
+        let emojiBytes = emojiError.toJSONBytes()
+        XCTAssertEqual(#"{"errorType":"error","errorMessage":"🥑👨‍👩‍👧‍👧👩‍👩‍👧‍👧👨‍👨‍👧"}"#, String(decoding: emojiBytes, as: Unicode.UTF8.self))
+    }
+
     class Behavior: LambdaServerBehavior {
         var state = 0