diff --git a/AFNetworking/AFHTTPRequestOperation.m b/AFNetworking/AFHTTPRequestOperation.m
index 80b61f8..4d9dd55 100644
--- a/AFNetworking/AFHTTPRequestOperation.m
+++ b/AFNetworking/AFHTTPRequestOperation.m
@@ -186,7 +186,7 @@ static void AFSwizzleClassMethodWithClassAndSelectorUsingBlock(Class klass, SEL
     }
 
     NSMutableURLRequest *mutableURLRequest = [self.request mutableCopy];
-    if ([[self.response allHeaderFields] valueForKey:@"ETag"]) {
+    if ([self.response respondsToSelector:@selector(allHeaderFields)] && [[self.response allHeaderFields] valueForKey:@"ETag"]) {
         [mutableURLRequest setValue:[[self.response allHeaderFields] valueForKey:@"ETag"] forHTTPHeaderField:@"If-Range"];
     }
     [mutableURLRequest setValue:[NSString stringWithFormat:@"bytes=%llu-", offset] forHTTPHeaderField:@"Range"];