diff --git a/Doc/Makefile b/Doc/Makefile
index 852bf50..a17ad81 100644
--- a/Doc/Makefile
+++ b/Doc/Makefile
@@ -83,6 +83,8 @@
 # $(shell) function here to work around that restriction by
 # identifying mkhowto and the commontex/ directory using absolute paths.
 #
+# If your doc build fails immediately, you may need to switch to GNU make.
+# (e.g. OpenBSD needs package gmake installed; use gmake instead of make)
 PWD=$(shell pwd)
 
 # (The trailing colon in the value is needed; TeX places it's default