diff --git a/README.md b/README.md
index c4bcf4d0..3561a5d0 100644
--- a/README.md
+++ b/README.md
@@ -167,7 +167,9 @@ be an Error instance.
 `withCredentials` in all XMLHttpRequests to use Cookies in requests. The
 remote server must accept CORS and credentials.
 * `chunkSize = Infinity`: a number indicating the maximum size of a chunk
-uploaded in a single request
+uploaded in a single request.  Note that if the server has hard limits (such as
+the minimum 5MB chunk size imposed by S3), specifying a chunk size which falls
+outside those hard limits will cause chunked uploads to fail
 * `metadata = {}`: an object with string values used as additional meta data
 which will be passed along to the server when (and only when) creating a new
 upload. Can be used for filenames, file types etc.