diff --git a/AFNetworking/AFHTTPRequestOperation.m b/AFNetworking/AFHTTPRequestOperation.m
index 1adea2b..98aa07c 100644
--- a/AFNetworking/AFHTTPRequestOperation.m
+++ b/AFNetworking/AFHTTPRequestOperation.m
@@ -107,18 +107,14 @@ static void AFSwizzleClassMethodWithClassAndSelectorUsingBlock(Class klass, SEL
 @property (readwrite, nonatomic, strong) NSURLRequest *request;
 @property (readwrite, nonatomic, strong) NSHTTPURLResponse *response;
 @property (readwrite, nonatomic, strong) NSError *HTTPError;
-@property (readwrite, nonatomic, copy) NSString *HTTPResponseString;
-@property (readwrite, nonatomic, strong) NSRecursiveLock *lock;
 @end
 
 @implementation AFHTTPRequestOperation
 @synthesize HTTPError = _HTTPError;
-@synthesize HTTPResponseString = _HTTPResponseString;
 @synthesize successCallbackQueue = _successCallbackQueue;
 @synthesize failureCallbackQueue = _failureCallbackQueue;
 @dynamic request;
 @dynamic response;
-@dynamic lock;
 
 - (void)dealloc {
     if (_successCallbackQueue) {
@@ -166,25 +162,19 @@ static void AFSwizzleClassMethodWithClassAndSelectorUsingBlock(Class klass, SEL
     }
 }
 
-- (NSString *)responseString {
-    [self.lock lock];
+- (NSStringEncoding)responseStringEncoding {
     // When no explicit charset parameter is provided by the sender, media subtypes of the "text" type are defined to have a default charset value of "ISO-8859-1" when received via HTTP. Data in character sets other than "ISO-8859-1" or its subsets MUST be labeled with an appropriate charset value.
     // See http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.4.1
-    if (!self.HTTPResponseString && self.response && !self.response.textEncodingName && self.responseData) {
+    if (self.response && !self.response.textEncodingName && self.responseData) {
         NSString *type = nil;
         AFGetMediaTypeAndSubtypeWithString([[self.response allHeaderFields] valueForKey:@"Content-Type"], &type, nil);
 
         if ([type isEqualToString:@"text"]) {
-            self.HTTPResponseString = [[NSString alloc] initWithData:self.responseData encoding:NSISOLatin1StringEncoding];
+            return NSISOLatin1StringEncoding;
         }
     }
-    [self.lock unlock];
 
-    if (self.HTTPResponseString) {
-        return self.HTTPResponseString;
-    } else {
-        return [super responseString];
-    }
+    return [super responseStringEncoding];
 }
 
 - (void)pause {