diff --git a/racket/src/cs/Makefile b/racket/src/cs/Makefile
index 51ff2faa7a..0c1bb2066c 100644
--- a/racket/src/cs/Makefile
+++ b/racket/src/cs/Makefile
@@ -4,7 +4,9 @@
 RACKET = ../../bin/racket
 SCHEME = scheme
 
-# Controls whether Racket layers are built as unsafe:
+# Controls whether Racket layers are built as unsafe; beware that
+# building some Racket libraries using safe mode may require setting
+# `PLT_CS_COMPILE_LIMIT` to 1000 (instead of 1000):
 UNSAFE_COMP = --unsafe
 
 # Controls whether compiled code is compressed: