diff --git a/README.md b/README.md
index 838607b..e622a83 100644
--- a/README.md
+++ b/README.md
@@ -47,7 +47,7 @@ The files are:
 
 First, edit `./config.mk` to match your local setup.
 
-In order to build XMenu you need the `Imlib2`, `Xlib` and `Xft` header files.
+In order to build XMenu you need the `Imlib2`, `Xlib`, `Xinerama` and `Xft` header files.
 The default configuration for XMenu is specified in the file `config.h`,
 you can edit it, but most configuration can be changed at runtime via
 X resources.  Enter the following command to build XMenu.  This command
diff --git a/config.mk b/config.mk
index eed2127..c14393c 100644
--- a/config.mk
+++ b/config.mk
@@ -8,6 +8,9 @@ MANPREFIX ?= ${PREFIX}/share/man
 LOCALINC ?= /usr/local/include
 LOCALLIB ?= /usr/local/lib
 
+# SHELL variable (mainly for non-GNU make)
+SHELL ?= /bin/sh
+
 X11INC ?= /usr/X11R6/include
 X11LIB ?= /usr/X11R6/lib