* configure.ac (FLEX_CXX_WORKS): New AM_CONDITIONAL.
* examples/calc++/local.mk (examples/calc++/calc++):
Build if FLEX_CXX_WORKS, not BISON_CXX_WORKS.
   AC_MSG_WARN([bypassing lex because flex is required])
   LEX=:
 }
+AM_CONDITIONAL([FLEX_CXX_WORKS],
+  [$LEX_IS_FLEX && test $bison_cv_cxx_works = yes])
 AC_PROG_YACC
 AC_PROG_RANLIB
 AC_PROG_GNU_M4
 
   $(calc_sources_extracted)                     \
   $(calc_sources_generated)
 
-if BISON_CXX_WORKS
+if FLEX_CXX_WORKS
 check_PROGRAMS += examples/calc++/calc++
 nodist_examples_calc___calc___SOURCES =         \
   $(calc_sources)