R: RCurl postForm() with Content-Length > 1024

Question

I'm having trouble POSTing data with Content-Length > 1024 using RCurl and postForm(). How can I increase the size limit of my HTTP request?

curl.opts <- list(httpheader = "Expect:",
                  httpheader = "Accept:text/xml",
                  verbose = TRUE,
                  followlocation = TRUE)

hmm <- postForm(myurl, longtxt=lotsoftext, 
               style = "POST", .opts = curl.opts)

Whenever Content-Length is < 1024 the server responds as it should, while > 1024 results in an error. Using "curl" from the command line on the other hand works fine also for long content.