diff --git a/docs/build.md b/docs/build.md
index a3b10b30..79a64324 100644
--- a/docs/build.md
+++ b/docs/build.md
@@ -4,7 +4,7 @@
 * npm: 4.x
 * node: 7.x
 
-You have to use `npm v4.x`, `v5.x` is not supported.
+You should use `npm v4.x` because `$ grand pre-build` fails on `v5.x`.
 
 ## Development