diff --git a/run-command.c b/run-command.c
index 84b883c213..3c3b8814df 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1246,6 +1246,15 @@ int finish_async(struct async *async)
 #endif
 }
 
+int async_with_fork(void)
+{
+#ifdef NO_PTHREADS
+	return 1;
+#else
+	return 0;
+#endif
+}
+
 const char *find_hook(const char *name)
 {
 	static struct strbuf path = STRBUF_INIT;
diff --git a/run-command.h b/run-command.h
index 9b7f38202c..68f5369fc2 100644
--- a/run-command.h
+++ b/run-command.h
@@ -141,6 +141,7 @@ struct async {
 int start_async(struct async *async);
 int finish_async(struct async *async);
 int in_async(void);
+int async_with_fork(void);
 void check_pipe(int err);
 
 /**
diff --git a/send-pack.c b/send-pack.c
index e920ca57df..f692686770 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -203,9 +203,8 @@ static int receive_status(int in, struct ref *refs)
 static int sideband_demux(int in, int out, void *data)
 {
 	int *fd = data, ret;
-#ifdef NO_PTHREADS
-	close(fd[1]);
-#endif
+	if (async_with_fork())
+		close(fd[1]);
 	ret = recv_sideband("send-pack", fd[0], out);
 	close(out);
 	return ret;