diff --git a/Sources/Core/AWSClientRuntime/Tests/AWSClientRuntimeTests/Protocols/AWSJSON/AWSJSONErrorTests.swift b/Sources/Core/AWSClientRuntime/Tests/AWSClientRuntimeTests/Protocols/AWSJSON/AWSJSONErrorTests.swift
new file mode 100644
index 00000000000..d08401c6295
--- /dev/null
+++ b/Sources/Core/AWSClientRuntime/Tests/AWSClientRuntimeTests/Protocols/AWSJSON/AWSJSONErrorTests.swift
@@ -0,0 +1,119 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+import SmithyTestUtil
+import SmithyHTTPAPI
+import Smithy
+@_spi(SmithyReadWrite) import class SmithyJSON.Reader
+@_spi(SmithyReadWrite) import struct AWSClientRuntime.AWSJSONError
+@_spi(SmithyReadWrite) import enum ClientRuntime.BaseErrorDecodeError
+import XCTest
+
+class AWSJSONErrorTests: HttpResponseTestBase {
+    // These error codes are taken from the examples in
+    // https://smithy.io/2.0/aws/protocols/aws-json-1_0-protocol.html#operation-error-serialization
+    // (one extra case with leading & trailing whitespace is added)
+    let errorCodes = [
+        "FooError",
+        "   FooError  ",
+        "FooError:http://internal.amazon.com/coral/com.amazon.coral.validate/",
+        "aws.protocoltests.restjson#FooError",
+        "aws.protocoltests.restjson#FooError:http://internal.amazon.com/coral/com.amazon.coral.validate/"
+    ]
+
+    // MARK: - error code decoding & sanitization
+
+    func test_errorInitThrowsIfNoCode() async throws {
+        let httpResponse = try httpResponseWithNoErrorCode()
+        let reader = try await Reader.from(data: httpResponse.body.readData() ?? Data())
+        XCTAssertThrowsError(try AWSJSONError(httpResponse: httpResponse, responseReader: reader, noErrorWrapping: true)) { error in
+            XCTAssertTrue((error as? BaseErrorDecodeError) == BaseErrorDecodeError.missingRequiredData)
+        }
+    }
+
+    func test_sanitizeErrorCodeInHeader() async throws {
+        for errorCode in errorCodes {
+            let httpResponse = try httpResponseWithHeaderErrorCode(errorCode: errorCode)
+            let reader = try await Reader.from(data: httpResponse.body.readData() ?? Data())
+            let awsJSONError = try AWSJSONError(httpResponse: httpResponse, responseReader: reader, noErrorWrapping: true)
+            XCTAssertEqual(awsJSONError.code, "FooError", "Error code '\(errorCode)' was not sanitized correctly, result was '\(awsJSONError.code)'")
+        }
+    }
+
+    func test_sanitizeErrorCodeInCodeField() async throws {
+        for errorCode in errorCodes {
+            let httpResponse = try httpResponseWithCodeFieldErrorCode(errorCode: errorCode)
+            let reader = try await Reader.from(data: httpResponse.body.readData() ?? Data())
+            let awsJSONError = try AWSJSONError(httpResponse: httpResponse, responseReader: reader, noErrorWrapping: true)
+            XCTAssertEqual(awsJSONError.code, "FooError", "Error code '\(errorCode)' was not sanitized correctly, result was '\(awsJSONError.code)'")
+        }
+    }
+
+    func test_sanitizeErrorCodeInTypeField() async throws {
+        for errorCode in errorCodes {
+            let httpResponse = try httpResponseWithTypeFieldErrorCode(errorCode: errorCode)
+            let reader = try await Reader.from(data: httpResponse.body.readData() ?? Data())
+            let awsJSONError = try AWSJSONError(httpResponse: httpResponse, responseReader: reader, noErrorWrapping: true)
+            XCTAssertEqual(awsJSONError.code, "FooError", "Error code '\(errorCode)' was not sanitized correctly, result was '\(awsJSONError.code)'")
+        }
+    }
+
+    // MARK: - Private methods
+
+    private func httpResponseWithNoErrorCode() throws -> HTTPResponse {
+        guard let response = buildHttpResponse(
+            code: 400,
+            headers: [
+                "Content-Type": "application/json",
+            ],
+            content: ByteStream.data(Data("{}".utf8))
+        ) else {
+            throw TestError("Something is wrong with the created http response")
+        }
+        return response
+    }
+
+    private func httpResponseWithHeaderErrorCode(errorCode: String) throws -> HTTPResponse {
+        guard let response = buildHttpResponse(
+            code: 400,
+            headers: [
+                "Content-Type": "application/json",
+                "X-Amzn-Errortype": errorCode,
+            ],
+            content: ByteStream.data(Data("{}".utf8))
+        ) else {
+            throw TestError("Something is wrong with the created http response")
+        }
+        return response
+    }
+
+    private func httpResponseWithCodeFieldErrorCode(errorCode: String) throws -> HTTPResponse {
+        guard let response = buildHttpResponse(
+            code: 400,
+            headers: [
+                "Content-Type": "application/json",
+            ],
+            content: ByteStream.data(Data("{\"code\":\"\(errorCode)\"}".utf8))
+        ) else {
+            throw TestError("Something is wrong with the created http response")
+        }
+        return response
+    }
+
+    private func httpResponseWithTypeFieldErrorCode(errorCode: String) throws -> HTTPResponse {
+        guard let response = buildHttpResponse(
+            code: 400,
+            headers: [
+                "Content-Type": "application/json",
+            ],
+            content: ByteStream.data(Data("{\"__type\":\"\(errorCode)\"}".utf8))
+        ) else {
+            throw TestError("Something is wrong with the created http response")
+        }
+        return response
+    }
+}
diff --git a/Sources/Core/AWSClientRuntime/Tests/AWSClientRuntimeTests/Protocols/RestJSON/RestJSONErrorTests.swift b/Sources/Core/AWSClientRuntime/Tests/AWSClientRuntimeTests/Protocols/RestJSON/RestJSONErrorTests.swift
index 5fc75aa8652..f51af9d8262 100644
--- a/Sources/Core/AWSClientRuntime/Tests/AWSClientRuntimeTests/Protocols/RestJSON/RestJSONErrorTests.swift
+++ b/Sources/Core/AWSClientRuntime/Tests/AWSClientRuntimeTests/Protocols/RestJSON/RestJSONErrorTests.swift
@@ -17,20 +17,7 @@ class RestJSONErrorTests: HttpResponseTestBase {
     let host = "myapi.host.com"
 
     func testRestJsonComplexError() async throws {
-        guard let httpResponse = buildHttpResponse(
-            code: 400,
-            headers: [
-                "Content-Type": "application/json",
-                "X-Header": "Header",
-                "X-Amzn-Errortype": "ComplexError"
-            ],
-            content: ByteStream.data("""
-            {\"TopLevel\": \"Top level\"}
-            """.data(using: .utf8))
-            ) else {
-                XCTFail("Something is wrong with the created http response")
-                return
-        }
+        let httpResponse = try httpResponse(errorCode: "my.protocoltests.restjson#ComplexError:http://my.fake.com")
 
         let greetingWithErrorsError = try await GreetingWithErrorsError.httpError(from:)(httpResponse)
 
@@ -47,16 +34,35 @@ class RestJSONErrorTests: HttpResponseTestBase {
         }
     }
 
-    func testSanitizeErrorName() {
-        let errorNames = [
+    private func httpResponse(errorCode: String) throws -> HTTPResponse {
+        guard let response = buildHttpResponse(
+            code: 400,
+            headers: [
+                "Content-Type": "application/json",
+                "X-Header": "Header",
+                "X-Amzn-Errortype": errorCode,
+            ],
+            content: ByteStream.data(Data("{\"TopLevel\": \"Top level\"}".utf8))
+        ) else {
+            throw TestError("Something is wrong with the created http response")
+        }
+        return response
+    }
+
+    func testSanitizeErrorName() async throws {
+        let errorCodes = [
+            "FooError",
             "   FooError  ",
-            "FooError:http://my.fake.com/",
-            "my.protocoltests.restjson#FooError",
-            "my.protocoltests.restjson#FooError:http://my.fake.com"
+            "FooError:http://internal.amazon.com/coral/com.amazon.coral.validate/",
+            "aws.protocoltests.restjson#FooError",
+            "aws.protocoltests.restjson#FooError:http://internal.amazon.com/coral/com.amazon.coral.validate/"
         ]
 
-        for errorName in errorNames {
-            XCTAssertEqual(sanitizeErrorType(errorName), "FooError")
+        for errorCode in errorCodes {
+            let httpResponse = try httpResponse(errorCode: errorCode)
+            let reader = try await Reader.from(data: httpResponse.body.readData() ?? Data())
+            let restJSONError = try RestJSONError(httpResponse: httpResponse, responseReader: reader, noErrorWrapping: true)
+            XCTAssertEqual(restJSONError.code, "FooError", "Error code '\(errorCode)' was not sanitized correctly, result was '\(restJSONError.code)'")
         }
     }
 }
diff --git a/Sources/Core/AWSClientRuntime/Tests/AWSClientRuntimeTests/TestError.swift b/Sources/Core/AWSClientRuntime/Tests/AWSClientRuntimeTests/TestError.swift
new file mode 100644
index 00000000000..3538407285d
--- /dev/null
+++ b/Sources/Core/AWSClientRuntime/Tests/AWSClientRuntimeTests/TestError.swift
@@ -0,0 +1,12 @@
+//
+// Copyright Amazon.com Inc. or its affiliates.
+// All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+struct TestError: Error {
+    let description: String
+
+    init(_ description: String) { self.description = description }
+}