diff --git a/README.md b/README.md
index 52d46e3..9e37e7d 100644
--- a/README.md
+++ b/README.md
@@ -221,6 +221,8 @@ The CacheableImage class returned by React Native Image Cache HOC includes a cou
 
 Use this method if you need to download a file to the local filesystem prior to rendering \<CacheableImage\> for some reason (perhaps to pre-warm the local cache). If calling this method repeatedly to cache a long list of files, be sure to use a queue and limit concurrency so your app performance does not suffer.
 
+**Note**: if you've set a custom `fileDirName` in your options, this will _not_ be used by `CacheableImage.cacheFile`. This means that you may end up downloading the image twice.
+
 ```js
 import imageCacheHoc from 'react-native-image-cache-hoc';
 const CacheableImage = imageCacheHoc(Image);
@@ -285,4 +287,4 @@ iOS only allows requests to https urls. If you need to load image files using ht
 
 > By default, iOS will block any request that's not encrypted using SSL. If you need to fetch from a cleartext URL (one that begins with http) you will first need to add an App Transport Security exception. If you know ahead of time what domains you will need access to, it is more secure to add exceptions just for those domains; if the domains are not known until runtime you can disable ATS completely. Note however that from January 2017, Apple's App Store review will require reasonable justification for disabling ATS.
 
-https://facebook.github.io/react-native/docs/network.html
\ No newline at end of file
+https://facebook.github.io/react-native/docs/network.html