diff --git a/AFNetworking/AFHTTPRequestOperation.m b/AFNetworking/AFHTTPRequestOperation.m
index 00e8c67..ec25ed0 100644
--- a/AFNetworking/AFHTTPRequestOperation.m
+++ b/AFNetworking/AFHTTPRequestOperation.m
@@ -31,6 +31,10 @@ NSSet * AFContentTypesFromHTTPHeader(NSString *string) {
         _skippedCharacterSet = [NSCharacterSet characterSetWithCharactersInString:@" ,"];
     });
     
+    if (!string) {
+        return nil;
+    }
+    
     NSScanner *scanner = [NSScanner scannerWithString:string];
     scanner.charactersToBeSkipped = _skippedCharacterSet;
     
@@ -226,7 +230,11 @@ static NSString * AFStringFromIndexSet(NSIndexSet *indexSet) {
 }
 
 + (BOOL)canProcessRequest:(NSURLRequest *)request {
-    return YES;
+    if (![[self class] isEqual:[AFHTTPRequestOperation class]]) {
+        return YES;
+    }
+    
+    return [[self acceptableContentTypes] intersectsSet:AFContentTypesFromHTTPHeader([request valueForHTTPHeaderField:@"Accept"])];
 }
 
 @end
diff --git a/AFNetworking/AFImageRequestOperation.m b/AFNetworking/AFImageRequestOperation.m
index 52426b1..ecfccd3 100644
--- a/AFNetworking/AFImageRequestOperation.m
+++ b/AFNetworking/AFImageRequestOperation.m
@@ -37,8 +37,6 @@ static dispatch_queue_t image_request_operation_processing_queue() {
 #elif __MAC_OS_X_VERSION_MIN_REQUIRED 
 @property (readwrite, nonatomic, retain) NSImage *responseImage;
 #endif
-
-+ (NSSet *)defaultAcceptablePathExtensions;
 @end
 
 @implementation AFImageRequestOperation
@@ -125,14 +123,6 @@ static dispatch_queue_t image_request_operation_processing_queue() {
 }
 #endif
 
-+ (NSSet *)acceptableContentTypes {
-    return [NSSet setWithObjects:@"image/tiff", @"image/jpeg", @"image/gif", @"image/png", @"image/ico", @"image/x-icon", @"image/bmp", @"image/x-bmp", @"image/x-xbitmap", @"image/x-win-bitmap", nil];
-}
-
-+ (NSSet *)defaultAcceptablePathExtensions {
-    return [NSSet setWithObjects:@"tif", @"tiff", @"jpg", @"jpeg", @"gif", @"png", @"ico", @"bmp", @"cur", nil];
-}
-
 - (id)initWithRequest:(NSURLRequest *)urlRequest {
     self = [super initWithRequest:urlRequest];
     if (!self) {
@@ -189,9 +179,6 @@ static dispatch_queue_t image_request_operation_processing_queue() {
 
 #pragma mark - AFHTTPClientOperation
 
-+ (BOOL)canProcessRequest:(NSURLRequest *)request {
-    return [[[self class] acceptableContentTypes] containsObject:[request valueForHTTPHeaderField:@"Accept"]] || [[self defaultAcceptablePathExtensions] containsObject:[[request URL] pathExtension]];
-}
 
 #if __IPHONE_OS_VERSION_MIN_REQUIRED
 + (AFHTTPRequestOperation *)HTTPRequestOperationWithRequest:(NSURLRequest *)urlRequest
@@ -217,6 +204,20 @@ static dispatch_queue_t image_request_operation_processing_queue() {
 }
 #endif
 
++ (NSSet *)acceptableContentTypes {
+    return [NSSet setWithObjects:@"image/tiff", @"image/jpeg", @"image/gif", @"image/png", @"image/ico", @"image/x-icon", @"image/bmp", @"image/x-bmp", @"image/x-xbitmap", @"image/x-win-bitmap", nil];
+}
+
++ (BOOL)canProcessRequest:(NSURLRequest *)request {
+    static NSSet * _acceptablePathExtension = nil;
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        _acceptablePathExtension = [[NSSet alloc] initWithObjects:@"tif", @"tiff", @"jpg", @"jpeg", @"gif", @"png", @"ico", @"bmp", @"cur", nil];
+    });
+    
+    return [_acceptablePathExtension containsObject:[[request URL] pathExtension]] || [super canProcessRequest:request];    
+}
+
 - (void)setCompletionBlockWithSuccess:(void (^)(AFHTTPRequestOperation *operation, id responseObject))success
                               failure:(void (^)(AFHTTPRequestOperation *operation, NSError *error))failure
 {
diff --git a/AFNetworking/AFJSONRequestOperation.m b/AFNetworking/AFJSONRequestOperation.m
index 651f2d7..451705e 100644
--- a/AFNetworking/AFJSONRequestOperation.m
+++ b/AFNetworking/AFJSONRequestOperation.m
@@ -35,8 +35,6 @@ static dispatch_queue_t json_request_operation_processing_queue() {
 @interface AFJSONRequestOperation ()
 @property (readwrite, nonatomic, retain) id responseJSON;
 @property (readwrite, nonatomic, retain) NSError *JSONError;
-
-+ (NSSet *)defaultAcceptablePathExtensions;
 @end
 
 @implementation AFJSONRequestOperation
@@ -61,18 +59,6 @@ static dispatch_queue_t json_request_operation_processing_queue() {
     return requestOperation;
 }
 
-+ (NSSet *)acceptableContentTypes {
-    return [NSSet setWithObjects:@"application/json", @"text/json", @"text/javascript", nil];
-}
-
-+ (NSSet *)defaultAcceptablePathExtensions {
-    return [NSSet setWithObjects:@"json", nil];
-}
-
-+ (BOOL)canProcessRequest:(NSURLRequest *)request {
-    return [[self acceptableContentTypes] containsObject:[request valueForHTTPHeaderField:@"Accept"]] || [[self defaultAcceptablePathExtensions] containsObject:[[request URL] pathExtension]];
-}
-
 - (void)dealloc {
     [_responseJSON release];
     [_JSONError release];
@@ -103,6 +89,16 @@ static dispatch_queue_t json_request_operation_processing_queue() {
     }
 }
 
+#pragma mark - AFHTTPRequestOperation
+
++ (NSSet *)acceptableContentTypes {
+    return [NSSet setWithObjects:@"application/json", @"text/json", @"text/javascript", nil];
+}
+
++ (BOOL)canProcessRequest:(NSURLRequest *)request {
+    return [[[request URL] pathExtension] isEqualToString:@"json"] || [super canProcessRequest:request];
+}
+
 - (void)setCompletionBlockWithSuccess:(void (^)(AFHTTPRequestOperation *operation, id responseObject))success
                               failure:(void (^)(AFHTTPRequestOperation *operation, NSError *error))failure
 {
diff --git a/AFNetworking/AFPropertyListRequestOperation.m b/AFNetworking/AFPropertyListRequestOperation.m
index b5609b3..ecca1af 100644
--- a/AFNetworking/AFPropertyListRequestOperation.m
+++ b/AFNetworking/AFPropertyListRequestOperation.m
@@ -35,8 +35,6 @@ static dispatch_queue_t property_list_request_operation_processing_queue() {
 @property (readwrite, nonatomic, retain) id responsePropertyList;
 @property (readwrite, nonatomic, assign) NSPropertyListFormat propertyListFormat;
 @property (readwrite, nonatomic, retain) NSError *propertyListError;
-
-+ (NSSet *)defaultAcceptablePathExtensions;
 @end
 
 @implementation AFPropertyListRequestOperation
@@ -63,14 +61,6 @@ static dispatch_queue_t property_list_request_operation_processing_queue() {
     return requestOperation;
 }
 
-+ (NSSet *)acceptableContentTypes {
-    return [NSSet setWithObjects:@"application/x-plist", nil];
-}
-
-+ (NSSet *)defaultAcceptablePathExtensions {
-    return [NSSet setWithObjects:@"plist", nil];
-}
-
 - (id)initWithRequest:(NSURLRequest *)urlRequest {
     self = [super initWithRequest:urlRequest];
     if (!self) {
@@ -108,8 +98,14 @@ static dispatch_queue_t property_list_request_operation_processing_queue() {
     }
 }
 
+#pragma mark - AFHTTPRequestOperation
+
++ (NSSet *)acceptableContentTypes {
+    return [NSSet setWithObjects:@"application/x-plist", nil];
+}
+
 + (BOOL)canProcessRequest:(NSURLRequest *)request {
-    return [[[self class] acceptableContentTypes] containsObject:[request valueForHTTPHeaderField:@"Accept"]] || [[self defaultAcceptablePathExtensions] containsObject:[[request URL] pathExtension]];
+    return [[[request URL] pathExtension] isEqualToString:@"plist"] || [super canProcessRequest:request];
 }
 
 - (void)setCompletionBlockWithSuccess:(void (^)(AFHTTPRequestOperation *operation, id responseObject))success
diff --git a/AFNetworking/AFXMLRequestOperation.m b/AFNetworking/AFXMLRequestOperation.m
index 25a3765..f40cacb 100644
--- a/AFNetworking/AFXMLRequestOperation.m
+++ b/AFNetworking/AFXMLRequestOperation.m
@@ -39,8 +39,6 @@ static dispatch_queue_t xml_request_operation_processing_queue() {
 @property (readwrite, nonatomic, retain) NSXMLDocument *responseXMLDocument;
 #endif
 @property (readwrite, nonatomic, retain) NSError *XMLError;
-
-+ (NSSet *)defaultAcceptablePathExtensions;
 @end
 
 @implementation AFXMLRequestOperation
@@ -90,14 +88,6 @@ static dispatch_queue_t xml_request_operation_processing_queue() {
 }
 #endif
 
-+ (NSSet *)acceptableContentTypes {
-    return [NSSet setWithObjects:@"application/xml", @"text/xml", nil];
-}
-
-+ (NSSet *)defaultAcceptablePathExtensions {
-    return [NSSet setWithObjects:@"xml", nil];
-}
-
 - (void)dealloc {
     [_responseXMLParser release];
     
@@ -146,8 +136,14 @@ static dispatch_queue_t xml_request_operation_processing_queue() {
     self.responseXMLParser.delegate = nil;
 }
 
+#pragma mark - AFHTTPRequestOperation
+
++ (NSSet *)acceptableContentTypes {
+    return [NSSet setWithObjects:@"application/xml", @"text/xml", nil];
+}
+
 + (BOOL)canProcessRequest:(NSURLRequest *)request {
-    return [[[self class] acceptableContentTypes] containsObject:[request valueForHTTPHeaderField:@"Accept"]] || [[self defaultAcceptablePathExtensions] containsObject:[[request URL] pathExtension]];
+    return [[[request URL] pathExtension] isEqualToString:@"xml"] || [super canProcessRequest:request];
 }
 
 - (void)setCompletionBlockWithSuccess:(void (^)(AFHTTPRequestOperation *operation, id responseObject))success