diff --git a/ChangeLog b/ChangeLog
index 14feb764..76e77c35 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2010-07-20  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
 
+	Fix parsing of empty variable settings on the command line.
+	* lib/autoconf/general.m4 (_AC_INIT_PARSE_ARGS): Work around
+	expr bug returning 0 instead of the empty string.
+	* lib/autotest/general.m4 (AT_INIT): Likewise.
+
 	Fix typo in the manual.
 	* doc/autoconf.texi (AC_ACT_IFELSE vs AC_TRY_ACT): Fix typo.
 
diff --git a/lib/autoconf/general.m4 b/lib/autoconf/general.m4
index 477c4ab8..bb188459 100644
--- a/lib/autoconf/general.m4
+++ b/lib/autoconf/general.m4
@@ -613,8 +613,9 @@ do
   fi
 
   case $ac_option in
-  *=*)	ac_optarg=`expr "X$ac_option" : '[[^=]]*=\(.*\)'` ;;
-  *)	ac_optarg=yes ;;
+  *=?*) ac_optarg=`expr "X$ac_option" : '[[^=]]*=\(.*\)'` ;;
+  *=)   ac_optarg= ;;
+  *)    ac_optarg=yes ;;
   esac
 
   # Accept the important Cygnus configure options, so we can diagnose typos.
diff --git a/lib/autotest/general.m4 b/lib/autotest/general.m4
index 2b46705f..e27d6011 100644
--- a/lib/autotest/general.m4
+++ b/lib/autotest/general.m4
@@ -474,8 +474,8 @@ do
   fi
 
   case $at_option in
-  *=*) at_optarg=`expr "x$at_option" : 'x[[^=]]*=\(.*\)'` ;;
-  *)   at_optarg= ;;
+  *=?*) at_optarg=`expr "X$at_option" : '[[^=]]*=\(.*\)'` ;;
+  *)    at_optarg= ;;
   esac
 
   # Accept the important Cygnus configure options, so we can diagnose typos.