diff --git a/AFNetworking/AFURLRequestSerialization.m b/AFNetworking/AFURLRequestSerialization.m
index 8679d97..37dab31 100755
--- a/AFNetworking/AFURLRequestSerialization.m
+++ b/AFNetworking/AFURLRequestSerialization.m
@@ -285,20 +285,20 @@ NSArray * AFQueryStringPairsFromKeyAndValue(NSString *key, id value) {
     __block AFStreamingMultipartFormData *formData = [[AFStreamingMultipartFormData alloc] initWithURLRequest:request stringEncoding:NSUTF8StringEncoding];
 
     if (parameters) {
-        [parameters enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL * __unused stop) {
+        for (AFQueryStringPair *pair in AFQueryStringPairsFromDictionary(parameters)) {
             NSData *data = nil;
-            if ([obj isKindOfClass:[NSData class]]) {
-                data = obj;
-            } else if ([obj isEqual:[NSNull null]]) {
+            if ([pair.value isKindOfClass:[NSData class]]) {
+                data = pair.value;
+            } else if ([pair.value isEqual:[NSNull null]]) {
                 data = [NSData data];
             } else {
-                data = [[obj description] dataUsingEncoding:NSUTF8StringEncoding];
+                data = [[pair.value description] dataUsingEncoding:self.stringEncoding];
             }
 
             if (data) {
-                [formData appendPartWithFormData:data name:[key description]];
+                [formData appendPartWithFormData:data name:[pair.field description]];
             }
-        }];
+        }
     }
 
     if (block) {