diff --git a/ChangeLog b/ChangeLog
index ecd5f4ee87..05ae770455 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Jun 21 15:54:55 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* configure.in: check if fork works with pthread.
+
 Sat Jun 21 15:31:09 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* tool/make-snapshot: ported to ruby.
diff --git a/configure.in b/configure.in
index c15d747bcc..da8518f440 100644
--- a/configure.in
+++ b/configure.in
@@ -766,6 +766,64 @@ AC_DEFINE_UNQUOTED([RUBY_SETJMP(env)], [${setjmp_prefix}setjmp(env${setjmp_sigma
 AC_DEFINE_UNQUOTED([RUBY_LONGJMP(env,val)], [${setjmp_prefix}longjmp(env,val)])
 AC_DEFINE_UNQUOTED(RUBY_JMP_BUF, ${setjmp_sigmask+${setjmp_prefix}}jmp_buf)
 
+
+case $target_os in
+*bsd*|darwin*)
+AC_CACHE_CHECK([if fork works with pthread], rb_cv_fork_with_pthread,
+[AC_TRY_RUN([
+#include <stdlib.h>
+#include <unistd.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <signal.h>
+
+void *
+thread_func(void *dmy)
+{
+    return dmy;
+}
+
+void *use_threads(void)
+{
+    pthread_t tid;
+    if (pthread_create(&tid, 0, thread_func, 0) != 0) {
+	exit(1);
+    }
+    if (pthread_join(tid, 0) != 0) {
+	exit(1);
+    }
+}
+
+int
+main(int argc, char *argv[])
+{
+    pid_t pid;
+    use_threads();
+    pid = fork();
+
+    if (pid) {
+	int loc;
+	sleep(1);
+	if (waitpid(pid, &loc, WNOHANG) == 0) {
+	    kill(pid, SIGKILL);
+	    return 1;
+	}
+    }
+    else {
+	use_threads();
+    }
+
+    return 0;
+}]
+	rb_cv_fork_with_pthread=yes,
+	rb_cv_fork_with_pthread=no,
+	rb_cv_fork_with_pthread=yes)])
+    ;;
+esac
+test x$rb_cv_fork_with_pthread = xyes || AC_DEFINE(CANNOT_FORK_WITH_PTHREAD)
+
 AC_ARG_ENABLE(setreuid,
        [  --enable-setreuid       use setreuid()/setregid() according to need even if obsolete.],
        [use_setreuid=$enableval])