diff --git a/Source/ARTFallback.h b/Source/ARTFallback.h
index 03b5f7989..9dc99a00e 100644
--- a/Source/ARTFallback.h
+++ b/Source/ARTFallback.h
@@ -20,6 +20,5 @@
  returns a random fallback host, returns null when all hosts have been popped.
  */
 -(NSString *) popFallbackHost;
-+(bool) shouldTryFallback:(ARTHttpResponse *) response  options:(ARTClientOptions *) options;
 
 @end
diff --git a/Source/ARTRest.m b/Source/ARTRest.m
index 5578ddaa1..c1d808e9c 100644
--- a/Source/ARTRest.m
+++ b/Source/ARTRest.m
@@ -136,27 +136,30 @@ - (void)executeRequest:(NSMutableURLRequest *)request completion:(void (^)(NSHTT
                 // Send it again, requesting a new token (forward callback)
                 [self.logger debug:__FILE__ line:__LINE__ message:@"requesting new token"];
                 [self executeRequest:request withAuthOption:ARTAuthenticationNewToken completion:callback];
-            } else if (callback) {
+                return;
+            } else {
                 // Return error with HTTP StatusCode if ARTErrorStatusCode does not exist
                 if (!dataError) {
                     dataError = [NSError errorWithDomain:ARTAblyErrorDomain code:response.statusCode userInfo:@{NSLocalizedDescriptionKey:[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]}];
                 }
-                callback(nil, nil, dataError);
+                error = dataError;
             }
-            return;
-        }
-        if (!blockFallbacks && [self shouldRetryWithFallback:request response:response error:error]) {
-            blockFallbacks = [[ARTFallback alloc] init];
         }
-        if (error && blockFallbacks) {
-            NSString *host = [blockFallbacks popFallbackHost];
-            if (host != nil) {
-                NSMutableURLRequest *newRequest = [request copy];
-                NSURL *url = request.URL;
-                NSString *urlStr = [NSString stringWithFormat:@"%@://%@:%@%@?%@", url.scheme, host, url.port, url.path, (url.query ? url.query : @"")];
-                newRequest.URL = [NSURL URLWithString:urlStr];
-                [self executeRequest:newRequest completion:callback fallbacks:fallbacks];
-                return;
+        if ([self shouldRetryWithFallback:request response:response error:error]) {
+            if (!blockFallbacks && [request.URL.host isEqualToString:[ARTDefault restHost]]) {
+                blockFallbacks = [[ARTFallback alloc] init];
+            }
+            if (blockFallbacks) {
+                NSString *host = [blockFallbacks popFallbackHost];
+                if (host != nil) {
+                    [self.logger debug:__FILE__ line:__LINE__ message:@"host is down; retrying request at %@", host];
+                    NSMutableURLRequest *newRequest = [request copy];
+                    NSURL *url = request.URL;
+                    NSString *urlStr = [NSString stringWithFormat:@"%@://%@:%@%@?%@", url.scheme, host, url.port, url.path, (url.query ? url.query : @"")];
+                    newRequest.URL = [NSURL URLWithString:urlStr];
+                    [self executeRequest:newRequest completion:callback fallbacks:fallbacks];
+                    return;
+                }
             }
         }
         if (callback) {
@@ -167,9 +170,6 @@ - (void)executeRequest:(NSMutableURLRequest *)request completion:(void (^)(NSHTT
 }
 
 - (BOOL)shouldRetryWithFallback:(NSMutableURLRequest *)request response:(NSHTTPURLResponse *)response error:(NSError *)error {
-    if (![request.URL.host isEqualToString:[ARTDefault restHost]]) {
-        return NO;
-    }
     if (response.statusCode >= 500 && response.statusCode <= 504) {
         return YES;
     }
diff --git a/Spec/RestClient.swift b/Spec/RestClient.swift
index 38b972eab..fe2e7ff55 100644
--- a/Spec/RestClient.swift
+++ b/Spec/RestClient.swift
@@ -535,6 +535,73 @@ class RestClient: QuickSpec {
 
             }
 
+            // RSC15
+            context("Host Fallback") {
+
+                // RSC15d
+                context("should use an alternative host when") {
+
+                    for caseTest: NetworkAnswer in [.HostUnreachable,
+                                                    .RequestTimeout(timeout: 0.1),
+                                                    .HostInternalError(code: 501)] {
+                        it("\(caseTest)") {
+                            let options = ARTClientOptions(key: "xxxx:xxxx")
+                            let client = ARTRest(options: options)
+                            client.httpExecutor = testHTTPExecutor
+                            testHTTPExecutor.http = MockHTTP(network: caseTest)
+                            let channel = client.channels.get("test")
+
+                            testHTTPExecutor.afterRequest = { _ in
+                                if testHTTPExecutor.requests.count == 2 {
+                                    // Stop
+                                    testHTTPExecutor.http = nil
+                                }
+                            }
+
+                            waitUntil(timeout: testTimeout) { done in
+                                channel.publish(nil, data: "nil") { _ in
+                                    done()
+                                }
+                            }
+
+                            expect(testHTTPExecutor.requests).to(haveCount(2))
+                            if testHTTPExecutor.requests.count != 2 {
+                                return
+                            }
+                            expect(NSRegularExpression.match(testHTTPExecutor.requests[0].URL!.absoluteString, pattern: "//rest.ably.io")).to(beTrue())
+                            expect(NSRegularExpression.match(testHTTPExecutor.requests[1].URL!.absoluteString, pattern: "//[a-e].ably-realtime.com")).to(beTrue())
+                        }
+                    }
+
+                }
+
+                // RSC15d
+                it("should not use an alternative host when the client receives an bad request") {
+                    let options = ARTClientOptions(key: "xxxx:xxxx")
+                    let client = ARTRest(options: options)
+                    client.httpExecutor = testHTTPExecutor
+                    testHTTPExecutor.http = MockHTTP(network: .Host400BadRequest)
+                    let channel = client.channels.get("test")
+
+                    testHTTPExecutor.afterRequest = { _ in
+                        if testHTTPExecutor.requests.count == 2 {
+                            // Stop
+                            testHTTPExecutor.http = nil
+                        }
+                    }
+
+                    waitUntil(timeout: testTimeout) { done in
+                        channel.publish(nil, data: "nil") { _ in
+                            done()
+                        }
+                    }
+
+                    expect(testHTTPExecutor.requests).to(haveCount(1))
+                    expect(NSRegularExpression.match(testHTTPExecutor.requests[0].URL!.absoluteString, pattern: "//rest.ably.io")).to(beTrue())
+                }
+
+            }
+
         } //RestClient
     }
 }
\ No newline at end of file
diff --git a/Spec/TestUtilities.swift b/Spec/TestUtilities.swift
index a84d06d17..06114ad05 100644
--- a/Spec/TestUtilities.swift
+++ b/Spec/TestUtilities.swift
@@ -500,6 +500,7 @@ enum NetworkAnswer {
     case HostUnreachable
     case RequestTimeout(timeout: NSTimeInterval)
     case HostInternalError(code: Int)
+    case Host400BadRequest
     case Custom(response: NSHTTPURLResponse?, data: NSData?, error: NSError?)
 }
 
@@ -524,6 +525,8 @@ class MockHTTP: ARTHttp {
                 }
             case .HostInternalError(let code):
                 callback?(NSHTTPURLResponse(URL: NSURL(string: "http://ios.test.suite")!, statusCode: code, HTTPVersion: nil, headerFields: nil), nil, nil)
+            case .Host400BadRequest:
+                callback?(NSHTTPURLResponse(URL: NSURL(string: "http://ios.test.suite")!, statusCode: 400, HTTPVersion: nil, headerFields: nil), nil, nil)
             case .Custom(let response, let data, let error):
                 callback?(response, data, error)
             }