diff --git a/ChangeLog b/ChangeLog
index e3fb344aa..5072a6026 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2010-05-28  Colin Watson  <cjwatson@ubuntu.com>
+
+	* configure.ac: AC_PROG_LEX sets LEX to ":" if lex is missing, not
+	to the empty string.
+
 2010-05-28  BVK Chaitanya  <bvk.groups@gmail.com>
 
 	Fix grub-emu issues on NetBSD, with gcc 4.1.3.
diff --git a/configure.ac b/configure.ac
index ace6bd81d..31b179d46 100644
--- a/configure.ac
+++ b/configure.ac
@@ -192,7 +192,7 @@ AC_PROG_LEX
 AC_PROG_MAKE_SET
 AC_PROG_MKDIR_P
 
-if test "x$LEX" = x; then
+if test "x$LEX" = "x:"; then
   AC_MSG_ERROR([flex is not found])
 else
   version=`$LEX --version | $AWK '{ split($NF,x,"."); print x[[1]]*10000+x[[2]]*100+x[[3]]; }'`