diff --git a/ChangeLog b/ChangeLog
index 90de0718..986c59fd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,6 +3,8 @@
 	* stk500v2.c: unreverse the argument order for
 	CMD_CHIP_ERASE_HVSP; Atmel says AVR068 is right, and
 	stk500.exe is wrong.
+	* configure.ac (AC_CHECK_LIB[usb]): Fix the generation
+	of HAVE_LIBUSB in ac_cfg.h.
 
 2006-08-17 Joerg Wunsch <j@uriah.heep.sax.de>
 
diff --git a/configure.ac b/configure.ac
index 6145959a..fe17d7e9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -47,7 +47,10 @@ AC_CHECK_LIB([readline], [readline])
 # usb_get_string_simple is only available in recent enough
 # versions of libusb, so use that as a decision base.
 AC_CHECK_LIB([usb], [usb_get_string_simple],
-		    [LIBUSB=-lusb],
+		    [LIBUSB=-lusb
+		    AC_DEFINE([HAVE_LIBUSB],
+		              [1],
+			      [Define to 1 if libusb is available.])],
 		    [LIBUSB=])
 AC_SUBST(LIBUSB, $LIBUSB)