diff --git a/NetworkingTests/Webservice/WebserviceTests.swift b/NetworkingTests/Webservice/WebserviceTests.swift
index aac4c2b..bf5c6eb 100644
--- a/NetworkingTests/Webservice/WebserviceTests.swift
+++ b/NetworkingTests/Webservice/WebserviceTests.swift
@@ -184,4 +184,44 @@ final class WebserviceTests: XCTestCase {
 
         waitForExpectations(timeout: 0.1, handler: nil)
     }
+
+    struct CancelRequestBehavior: RequestBehavior {
+        func allowCompletion(data: Data?, response: URLResponse?, error: Error?) -> Bool {
+            return false
+        }
+
+        func after(completion result: Result<HTTPURLResponse, Error>) {
+            switch result {
+            case .success:
+                XCTFail("should not get called")
+            case .failure(let error):
+                if case Webservice.Error.cancelled = error {
+                    print("request cancelled")
+                } else {
+                    XCTFail("incorrect error")
+                }
+            }
+        }
+    }
+
+    func testCancelledBehavior() {
+
+        let sessionMock = URLSessionDataTaskLoaderFake(data: nil,
+                                                       response: HTTPURLResponse(url: URL.fake(),
+                                                                                 statusCode: 200,
+                                                                                 httpVersion: nil,
+                                                                                 headerFields: nil),
+                                                       error: nil)
+
+        webservice = Webservice(baseURL: URL.fake(),
+                                session: sessionMock,
+                                defaultRequestBehavior: CancelRequestBehavior())
+
+        let resource = Resource<Empty, Empty>(endpoint: "/", decoder: EmptyDecoder())
+
+        webservice.load(resource) { _ in
+            XCTFail("completion should not get called")
+        }
+    }
 }
+
diff --git a/Sources/Webservice/Requests/RequestBehavior.swift b/Sources/Webservice/Requests/RequestBehavior.swift
index 091f4e2..2a801ae 100644
--- a/Sources/Webservice/Requests/RequestBehavior.swift
+++ b/Sources/Webservice/Requests/RequestBehavior.swift
@@ -4,16 +4,17 @@ public protocol RequestBehavior {
     func modify(urlComponents: URLComponents) -> URLComponents
     func modify(planned request: URLRequest) -> URLRequest
     func before(sending request: URLRequest)
-
     func modifyResponse(data: Data?, response: URLResponse?, error: Error?) -> (Data?, URLResponse?, Error?)
+    func allowCompletion(data: Data?, response: URLResponse?, error: Error?) -> Bool
     func after(completion result: Result<HTTPURLResponse, Error>)
+
 }
 
 public extension RequestBehavior {
     func modify(urlComponents: URLComponents) -> URLComponents { return urlComponents }
     func modify(planned request: URLRequest) -> URLRequest { return request }
     func before(sending: URLRequest) {}
-
+    func allowCompletion(data: Data?, response: URLResponse?, error: Error?) -> Bool { return true }
     func modifyResponse(data: Data?, response: URLResponse?, error: Error?)
         -> (Data?, URLResponse?, Error?) { return (data, response, error) }
     func after(completion result: Result<HTTPURLResponse, Error>) {}
@@ -74,4 +75,13 @@ private struct CompoundRequestBehavior: RequestBehavior {
             $0.after(completion: result)
         }
     }
+
+    func allowCompletion(data: Data?, response: URLResponse?, error: Error?) -> Bool {
+        for behaviour in behaviors {
+            if !behaviour.allowCompletion(data: data, response: response, error: error) {
+                return false
+            }
+        }
+        return true
+    }
 }
diff --git a/Sources/Webservice/Webservice.swift b/Sources/Webservice/Webservice.swift
index ed364c7..559354e 100644
--- a/Sources/Webservice/Webservice.swift
+++ b/Sources/Webservice/Webservice.swift
@@ -14,6 +14,7 @@ public struct Webservice: ResourceRequestable {
     public enum Error: Swift.Error {
         case http(HTTP.StatusCode, Swift.Error?)
         case unknown(Swift.Error?)
+        case cancelled
     }
 
     private let baseURL: URL
@@ -42,6 +43,12 @@ public struct Webservice: ResourceRequestable {
             requestBehavior.before(sending: request)
 
             session.dataTask(with: request) { data, response, error in
+
+                guard requestBehavior.allowCompletion(data: data, response: response, error: error) else {
+                    requestBehavior.after(completion: Result.failure(Error.cancelled))
+                    return
+                }
+
                 let (data, response, error) = requestBehavior.modifyResponse(data: data,
                                                                              response: response,
                                                                              error: error)