diff --git a/AFNetworking/AFURLConnectionOperation.h b/AFNetworking/AFURLConnectionOperation.h
index 210ac43..1491f20 100644
--- a/AFNetworking/AFURLConnectionOperation.h
+++ b/AFNetworking/AFURLConnectionOperation.h
@@ -128,7 +128,7 @@ extern NSString * const AFNetworkingOperationDidFinishNotification;
 /**
  The string representation of the response data.
  
- @discussion This method uses the string encoding of the response to construct a string from the response data.
+ @discussion This method uses the string encoding of the response, or if UTF-8 if not specified, to construct a string from the response data.
  */
 @property (readonly, nonatomic, copy) NSString *responseString;
 
diff --git a/AFNetworking/AFURLConnectionOperation.m b/AFNetworking/AFURLConnectionOperation.m
index 97bf745..3869bb9 100644
--- a/AFNetworking/AFURLConnectionOperation.m
+++ b/AFNetworking/AFURLConnectionOperation.m
@@ -233,7 +233,11 @@ static inline NSString * AFKeyPathFromOperationState(AFOperationState state) {
 
 - (NSString *)responseString {
     if (!_responseString && self.response && self.responseData) {
-        NSStringEncoding textEncoding = CFStringConvertEncodingToNSStringEncoding(CFStringConvertIANACharSetNameToEncoding((CFStringRef)self.response.textEncodingName));
+        NSStringEncoding textEncoding = NSUTF8StringEncoding;
+        if (self.response.textEncodingName) {
+            textEncoding = CFStringConvertEncodingToNSStringEncoding(CFStringConvertIANACharSetNameToEncoding((CFStringRef)self.response.textEncodingName));
+        }
+        
         self.responseString = [[[NSString alloc] initWithData:self.responseData encoding:textEncoding] autorelease];
     }