diff --git a/builds/unix/configure.raw b/builds/unix/configure.raw
index b3ced0509..45a9be6e4 100644
--- a/builds/unix/configure.raw
+++ b/builds/unix/configure.raw
@@ -1112,21 +1112,26 @@ AC_SUBST([wl])
 AC_SUBST([build_libtool_libs])
 
 
-# changing LDFLAGS value should only be done after
-# lt_cv_prog_compiler_static_works test
+# We cannot use alternation (`\|`) in the `sed` regexp since it is not
+# portable.
 
 ftoption_set()
 {
-  regexp="-e \\\"s|.*#.*def.*$1\>.*|#define $1|\\\""
+  regexp="-e \\\"s|.*#.*def.*$1 .*|#define $1|\\\" \
+          -e \\\"s|.*#.*def.*$1\$|#define $1|\\\""
   FTOPTION_H_SED="$FTOPTION_H_SED $regexp"
 }
 
 ftoption_unset()
 {
-  regexp="-e \\\"s|.*#.*def.*$1\>.*|/* #undef $1 */|\\\""
+  regexp="-e \\\"s|.*#.*def.*$1 .*|/* #undef $1 */|\\\" \
+          -e \\\"s|.*#.*def.*$1\$|/* #undef $1 */|\\\""
   FTOPTION_H_SED="$FTOPTION_H_SED $regexp"
 }
 
+# Changing the `LDFLAGS` value should only be done after the
+# `lt_cv_prog_compiler_static_works` test.
+
 if test "$have_zlib" != no; then
   CFLAGS="$CFLAGS $ZLIB_CFLAGS"
   LDFLAGS="$LDFLAGS $ZLIB_LIBS"