diff --git a/README.md b/README.md
index 64893a1..24b6cb1 100644
--- a/README.md
+++ b/README.md
@@ -51,3 +51,8 @@ Put your SUBDIRS before your include lines.  You really are supposed to do this
 buildsys *anyway*, but for some reason it sometimes lets you put it after the fact.
 
 My fork does not let you do that as SUBDIRS are turned into make tasks.
+
+#### It doesn't work with FreeBSD make, NetBSD make, or some other non-GNU make
+
+Sorry, but in order to avoid using the shell unnecessarily, we have to depend on
+GNU-make specific behaviour.  Use gmake instead.