diff --git a/README.md b/README.md
index ca84bf1..455fe62 100644
--- a/README.md
+++ b/README.md
@@ -58,7 +58,8 @@ Majors available for evancz/elm-html: [4.0.2, 4.0.1, 4.0.0]
 
 ## elm_deps_sync
 
-Sometimes we want to sync the deps between two files, such that all the deps in one file are matched in another file
+Sometimes we want to sync the deps between two files, such that all the deps in one file are matched in another file.
+The deps in the first file will be added to the deps in the second file. Note that this is additive.
 
 Usage: