diff --git a/engine/src/flutter/HACKING.md b/engine/src/flutter/HACKING.md
index b63654e17b2..e53c80d69d9 100644
--- a/engine/src/flutter/HACKING.md
+++ b/engine/src/flutter/HACKING.md
@@ -5,7 +5,7 @@ Building
 --------
 
 * Follow the setup & build instructions for [mojo](https://github.com/domokit/mojo)
-* Build ``sky`` with ``ninja``, e.g. ``ninja C out/Debug sky``
+* Build ``sky`` with ``ninja``, e.g. ``ninja -C out/Debug sky``
 
 Running applications
 --------------------