diff --git a/AFNetworking/AFJSONRequestOperation.m b/AFNetworking/AFJSONRequestOperation.m
index 78f3bb2..5401cbf 100644
--- a/AFNetworking/AFJSONRequestOperation.m
+++ b/AFNetworking/AFJSONRequestOperation.m
@@ -64,7 +64,9 @@ static dispatch_queue_t json_request_operation_processing_queue() {
     if (!_responseJSON && [self.responseData length] > 0 && [self isFinished] && !self.JSONError) {
         NSError *error = nil;
 
-        if ([self.responseData length] == 0) {
+        // Workaround for behavior of Rails to return a single space for `head :ok` (a workaround for a bug in Safari), which is not interpreted as valid input by NSJSONSerialization.
+        // See https://github.com/rails/rails/issues/1742
+        if ([self.responseData length] == 0 || [self.responseString isEqualToString:@" "]) {
             self.responseJSON = nil;
         } else {
             // Workaround for a bug in NSJSONSerialization when Unicode character escape codes are used instead of the actual character