:: commit 820921a424346e7d6100db949247637cf62f5654

diff --git a/Makefile b/Makefile
index db907fef..7d56ebe2 100644
--- a/Makefile
+++ b/Makefile
@@ -1,3 +1,7 @@
+ifneq (,)
+This makefile requires GNU Make.
+endif
+
 PREFIX ?= /usr/local
 DESTDIR ?=
 
diff --git a/decompressor/Makefile b/decompressor/Makefile
index 2ae358a6..bebfe471 100644
--- a/decompressor/Makefile
+++ b/decompressor/Makefile
@@ -1,3 +1,7 @@
+ifneq (,)
+This makefile requires GNU Make.
+endif
+
 BUILDDIR =
 
 ifeq ($(BUILDDIR), )
diff --git a/stage23/Makefile b/stage23/Makefile
index e2b4fb15..e266db20 100644
--- a/stage23/Makefile
+++ b/stage23/Makefile
@@ -1,3 +1,7 @@
+ifneq (,)
+This makefile requires GNU Make.
+endif
+
 TARGET =
 BUILDDIR =