diff --git a/HACKING.adoc b/HACKING.adoc
index 3e4d738d9806..360fab104d95 100644
--- a/HACKING.adoc
+++ b/HACKING.adoc
@@ -30,7 +30,12 @@ make world.opt
 make runtop
 ----
 
-4. Hack frenetically and keep rebuilding.
+4. Hack frenetically and keep rebuilding. You can speed up future builds
+by using ocamlc.opt to compile the compiler:
++
+----
+cp ocamlc.opt boot/
+----
 
 5. Run the testsuite from time to time.
 +