diff --git a/scripts/makefile.mingw b/scripts/makefile.mingw
index 59b5b0cad..fac013d96 100644
--- a/scripts/makefile.mingw
+++ b/scripts/makefile.mingw
@@ -14,6 +14,10 @@
 
 # Built from makefile.cygwin
 
+# This makefile expects to be run under the MSYS shell (part of
+# the MINGW project) and not under CMD.EXE which does not provide
+# "cat" or "sed".
+
 # This makefile intends to support building outside the src directory
 # if desired. When invoking it, specify an argument to SRCDIR on the
 # command line that points to the top of the directory where your source