diff --git a/configure b/configure
index 6f8c6ed5c..a85c7eaf0 100755
--- a/configure
+++ b/configure
@@ -2672,7 +2672,7 @@ fi
 if test "$ac_cv_header_regex_h" = yes ||
    test "$ac_cv_header_rxposix_h" = yes ||
    test "$ac_cv_header_rx_rxposix_h" = yes; then
-  unset ac_cv_func_regcomp
+  ac_cv_func_regcomp=
   echo $ac_n "checking for regcomp""... $ac_c" 1>&6
 echo "configure:2678: checking for regcomp" >&5
 if eval "test \"`echo '$''{'ac_cv_func_regcomp'+set}'`\" = set"; then
@@ -2765,7 +2765,7 @@ else
   echo "$ac_t""no" 1>&6
 fi
 
-    unset ac_cv_func_regcomp
+    ac_cv_func_regcomp=
     echo $ac_n "checking for regcomp""... $ac_c" 1>&6
 echo "configure:2771: checking for regcomp" >&5
 if eval "test \"`echo '$''{'ac_cv_func_regcomp'+set}'`\" = set"; then
diff --git a/configure.in b/configure.in
index 1c8e8bb42..ebc4299f0 100644
--- a/configure.in
+++ b/configure.in
@@ -139,11 +139,11 @@ fi
 if test "$ac_cv_header_regex_h" = yes ||
    test "$ac_cv_header_rxposix_h" = yes ||
    test "$ac_cv_header_rx_rxposix_h" = yes; then
-  unset ac_cv_func_regcomp
+  ac_cv_func_regcomp=
   AC_CHECK_FUNC(regcomp, [LIBOBJS="regex-posix.o $LIBOBJS"])
   if test "$ac_cv_func_regcomp" != yes; then
     AC_CHECK_LIB(rx, main)
-    unset ac_cv_func_regcomp
+    ac_cv_func_regcomp=
     AC_CHECK_FUNC(regcomp, [LIBOBJS="regex-posix.o $LIBOBJS"])
   fi
   dnl The following should not be necessary, but for some reason