diff -r 2cc5ed6e6255 -r 244d8c60b997 configure.ac
--- a/configure.ac	Mon Jul 07 15:20:43 2008 +0100
+++ b/configure.ac	Thu Jul 10 18:53:00 2008 +0100
@@ -32,7 +32,16 @@
   export PKG_CONFIG_PATH="$with_lemon/lib/pkgconfig/:$PKG_CONFIG_PATH"
 fi
 
-PKG_CHECK_MODULES([LEMON], [lemon >= 0.6.90])
+PKG_CHECK_MODULES([LEMON], [lemon >= 0.6.90], [], [AC_MSG_ERROR([
+No appropriate version of package 'lemon' found.
+
+Consider adjusting the PKG_CONFIG_PATH environment variable or using
+the --with-lemon=PREFIX configure flag if you installed it in a
+non-standard prefix.
+
+Alternatively, you may set the environment variables LEMON_CFLAGS and
+LEMON_LIBS to avoid the need to call pkg-config.  See the pkg-config
+man page for more details.])])
 
 dnl Checks for header files.
 AC_CHECK_HEADERS([libintl.h locale.h])