diff --git a/AFNetworking/AFHTTPClient.m b/AFNetworking/AFHTTPClient.m
index d302478..3981be6 100644
--- a/AFNetworking/AFHTTPClient.m
+++ b/AFNetworking/AFHTTPClient.m
@@ -116,9 +116,9 @@ static NSString * AFPercentEscapedQueryStringPairMemberFromStringWithEncoding(NS
 
 - (NSString *)URLEncodedStringValueWithEncoding:(NSStringEncoding)stringEncoding {
     if (!self.value || [self.value isEqual:[NSNull null]]) {
-        return AFPercentEscapedQueryStringPairMemberFromStringWithEncoding(self.field, stringEncoding);
+        return AFPercentEscapedQueryStringPairMemberFromStringWithEncoding([self.field description], stringEncoding);
     } else {
-        return [NSString stringWithFormat:@"%@=%@", AFPercentEscapedQueryStringPairMemberFromStringWithEncoding(self.field, stringEncoding), AFPercentEscapedQueryStringPairMemberFromStringWithEncoding([self.value description], stringEncoding)];
+        return [NSString stringWithFormat:@"%@=%@", AFPercentEscapedQueryStringPairMemberFromStringWithEncoding([self.field description], stringEncoding), AFPercentEscapedQueryStringPairMemberFromStringWithEncoding([self.value description], stringEncoding)];
     }
 }