diff -pU3 a/configure b/configure
--- a/configure	2017-09-14 21:09:29.000000000 +0900
+++ b/configure	2017-09-15 05:56:46.000000000 +0900
@@ -10366,6 +10366,7 @@ fi
 ac_res=$ac_cv_search___gmpz_init
 if test "$ac_res" != no; then :
   test "$ac_res" = "none required" || LIBS="$ac_res $LIBS"
+  $as_echo "#define HAVE_LIBGMP 1" >>confdefs.h
 
 fi
 
@@ -10435,6 +10436,7 @@ fi
 ac_res=$ac_cv_search_malloc_conf
 if test "$ac_res" != no; then :
   test "$ac_res" = "none required" || LIBS="$ac_res $LIBS"
+  $as_echo "#define HAVE_LIBJEMALLOC 1" >>confdefs.h
 
 else
   with_jemalloc=no
diff -pU3 a/configure.in b/configure.in
--- a/configure.in	2017-08-09 19:28:56.000000000 +0900
+++ b/configure.in	2017-09-15 07:18:25.000000000 +0900
@@ -1337,13 +1337,15 @@ AC_ARG_WITH([gmp],
 AS_IF([test "x$with_gmp" != xno],
   [AC_CHECK_HEADERS(gmp.h)
    AS_IF([test "x$ac_cv_header_gmp_h" != xno],
-     AC_SEARCH_LIBS([__gmpz_init], [gmp]))])
+     AC_SEARCH_LIBS([__gmpz_init], [gmp],
+       [AC_DEFINE(HAVE_LIBGMP, 1)]))])
 
 AC_ARG_WITH([jemalloc],
   [AS_HELP_STRING([--with-jemalloc],[use jemalloc allocator])],
   [with_jemalloc=$withval], [with_jemalloc=no])
 AS_IF([test "x$with_jemalloc" = xyes],[
-  AC_SEARCH_LIBS([malloc_conf], [jemalloc], [], [with_jemalloc=no])
+  AC_SEARCH_LIBS([malloc_conf], [jemalloc],
+    [AC_DEFINE(HAVE_LIBJEMALLOC, 1)], [with_jemalloc=no])
   AC_CHECK_HEADER(jemalloc/jemalloc.h, [
     AC_DEFINE(RUBY_ALTERNATIVE_MALLOC_HEADER, [<jemalloc/jemalloc.h>])
   ])