diff --git a/git-fat b/git-fat
index 8b88054..2ed592b 100755
--- a/git-fat
+++ b/git-fat
@@ -146,7 +146,7 @@ except ImportError:
     class S3Backend(object):
 
         def __init__(self,bucket,key,secret,objdir):
-            raise RuntimeError("S3Backend requires boto.")
+            raise RuntimeError("S3Backend requires boto and filechunkio.")
 
 BLOCK_SIZE = 4096
 LARGE_FILE_SIZE = 4294967296    # consider > 4GBs is large file size(Current limitation in windows)