diff --git a/Sources/FoundationNetworking/URLSession/NetworkingSpecific.swift b/Sources/FoundationNetworking/URLSession/NetworkingSpecific.swift
index 4057cbab56..419c9ddb43 100644
--- a/Sources/FoundationNetworking/URLSession/NetworkingSpecific.swift
+++ b/Sources/FoundationNetworking/URLSession/NetworkingSpecific.swift
@@ -40,6 +40,15 @@ class _NSNonfileURLContentLoader: _NSNonfileURLContentLoading {
     
     @usableFromInline
     func contentsOf(url: URL) throws -> (result: NSData, textEncodingNameIfAvailable: String?) {
+
+        func cocoaError(with error: Error? = nil) -> Error {
+            var userInfo: [String: Any] = [:]
+            if let error = error {
+                userInfo[NSUnderlyingErrorKey] = error
+            }
+            return CocoaError.error(.fileReadUnknown, userInfo: userInfo, url: url)
+        }
+
         var urlResponse: URLResponse?
         let session = URLSession(configuration: URLSessionConfiguration.default)
         let cond = NSCondition()
@@ -63,10 +72,25 @@ class _NSNonfileURLContentLoader: _NSNonfileURLContentLoading {
             cond.wait()
         }
         cond.unlock()
-        
+
+        guard resError == nil else {
+            throw cocoaError(with: resError)
+        }
+
         guard let data = resData else {
-            throw resError!
+            throw cocoaError()
+        }
+
+        if let statusCode = (urlResponse as? HTTPURLResponse)?.statusCode {
+            switch statusCode {
+                // These are the only valid response codes that data will be returned for, all other codes will be treated as error.
+                case 101, 200...399, 401, 407:
+                    return (NSData(bytes: UnsafeMutableRawPointer(mutating: (data as NSData).bytes), length: data.count), urlResponse?.textEncodingName)
+
+                default:
+                    break
+            }
         }
-        return (NSData(bytes: UnsafeMutableRawPointer(mutating: (data as NSData).bytes), length: data.count), urlResponse?.textEncodingName)
+        throw cocoaError()
     }
 }
diff --git a/Tests/Foundation/HTTPServer.swift b/Tests/Foundation/HTTPServer.swift
index 9b864f4c92..53d41d5ef9 100644
--- a/Tests/Foundation/HTTPServer.swift
+++ b/Tests/Foundation/HTTPServer.swift
@@ -716,7 +716,11 @@ public class TestURLSessionServer {
                                  bodyData: helloWorld)
         }
 
-        return _HTTPResponse(response: .OK, body: capitals[String(uri.dropFirst())]!)
+        guard let capital = capitals[String(uri.dropFirst())] else {
+            return _HTTPResponse(response: .NOTFOUND, body: "Not Found")
+        }
+        return _HTTPResponse(response: .OK, body: capital)
+
     }
 }
 
diff --git a/Tests/Foundation/Tests/TestNSData.swift b/Tests/Foundation/Tests/TestNSData.swift
index fb8dba5aa0..133af6a95b 100644
--- a/Tests/Foundation/Tests/TestNSData.swift
+++ b/Tests/Foundation/Tests/TestNSData.swift
@@ -1517,13 +1517,44 @@ extension TestNSData {
 #endif
     }
 
-    func test_contentsOfURL() {
-        let urlString = "http://127.0.0.1:\(TestURLSession.serverPort)/country.txt"
-        let url = URL(string: urlString)!
-        let contents = NSData(contentsOf: url)
-        XCTAssertNotNil(contents)
-        if let contents = contents {
-            XCTAssertTrue(contents.length > 0)
+    func test_contentsOfURL() throws {
+        do {
+            let urlString = "http://127.0.0.1:\(TestURLSession.serverPort)/country.txt"
+            let url = try XCTUnwrap(URL(string: urlString))
+            let contents = NSData(contentsOf: url)
+            XCTAssertNotNil(contents)
+            if let contents = contents {
+                XCTAssertTrue(contents.length > 0)
+            }
+        }
+
+        do {
+            let urlString = "http://127.0.0.1:\(TestURLSession.serverPort)/NotFound"
+            let url = try XCTUnwrap(URL(string: urlString))
+            XCTAssertNil(NSData(contentsOf: url))
+            do {
+                _ = try NSData(contentsOf: url, options: [])
+                XCTFail("NSData(contentsOf:options: did not throw")
+            } catch let error as NSError {
+                if let nserror = error as? NSError {
+                    XCTAssertEqual(NSCocoaErrorDomain, nserror.domain)
+                    XCTAssertEqual(CocoaError.fileReadUnknown.rawValue, nserror.code)
+                } else {
+                    XCTFail("Not an NSError")
+                }
+            }
+
+            do {
+                _ = try Data(contentsOf: url)
+                XCTFail("Data(contentsOf:options: did not throw")
+            } catch let error as NSError {
+                if let nserror = error as? NSError {
+                    XCTAssertEqual(NSCocoaErrorDomain, nserror.domain)
+                    XCTAssertEqual(CocoaError.fileReadUnknown.rawValue, nserror.code)
+                } else {
+                    XCTFail("Not an NSError")
+                }
+            }
         }
     }