diff --git a/src/configure.ac b/src/configure.ac
index fc346dc..93fbc32 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -4588,8 +4588,8 @@
   dnl And undefine it first to avoid a warning.
   AC_MSG_CHECKING(whether we need -D_FORTIFY_SOURCE=1)
   if test "$gccmajor" -gt "3"; then
-    CFLAGS=`echo "$CFLAGS" | sed -e 's/-D_FORTIFY_SOURCE=.,//g' -e 's/ *-Wp,-D_FORTIFY_SOURCE=. / /g' -e 's/,-D_FORTIFY_SOURCE=. //g' -e 's/ *-D_FORTIFY_SOURCE=.//g' -e 's/ *-U_FORTIFY_SOURCE//g' -e 's/$/ -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1/'`
-    CPPFLAGS=`echo "$CPPFLAGS" | sed -e 's/-D_FORTIFY_SOURCE=.,//g' -e 's/ *-Wp,-D_FORTIFY_SOURCE=. / /g' -e 's/,-D_FORTIFY_SOURCE=. //g' -e 's/ *-D_FORTIFY_SOURCE=.//g' -e 's/ *-U_FORTIFY_SOURCE//g'`
+    CFLAGS=`echo "$CFLAGS" | sed -e 's/-D_FORTIFY_SOURCE=.,//g' -e 's/ *-Wp,-D_FORTIFY_SOURCE=. / /g' -e 's/,-D_FORTIFY_SOURCE=. //g' -e 's/ *-D_FORTIFY_SOURCE=.//g' -e 's/ *-Wp,-U_FORTIFY_SOURCE//g' -e 's/ *-U_FORTIFY_SOURCE//g' -e 's/$/ -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1/'`
+    CPPFLAGS=`echo "$CPPFLAGS" | sed -e 's/-D_FORTIFY_SOURCE=.,//g' -e 's/ *-Wp,-D_FORTIFY_SOURCE=. / /g' -e 's/,-D_FORTIFY_SOURCE=. //g' -e 's/ *-D_FORTIFY_SOURCE=.//g' -e 's/ *-Wp,-U_FORTIFY_SOURCE//g' -e 's/ *-U_FORTIFY_SOURCE//g'`
     AC_MSG_RESULT(yes)
   else
     AC_MSG_RESULT(no)