diff --git a/src/server/client.c b/src/server/client.c
index 6d8543b..eb203b3 100644
--- a/src/server/client.c
+++ b/src/server/client.c
@@ -500,7 +500,7 @@ void client_reply_to_flush( struct client* client, struct nbd_request request )
 	debug("request flush from=%"PRIu64", len=%"PRIu32", handle=0x%08X", request.from, request.len, request.handle);
 
 	ERROR_IF_NEGATIVE(
-		fsync(client->fileno),
+		msync(client->mapped, client->mapped_size, MS_SYNC | MS_INVALIDATE),
 		"flush failed"
 	);
 
@@ -697,7 +697,7 @@ void* client_serve(void* client_uncast)
 		open_and_mmap(
 			client->serve->filename,
 			&client->fileno,
-			NULL,
+			&client->mapped_size,
 			(void**) &client->mapped
 		),
 		"Couldn't open/mmap file %s: %s", client->serve->filename, strerror( errno )
diff --git a/src/server/client.h b/src/server/client.h
index 9110d7d..a03ea44 100644
--- a/src/server/client.h
+++ b/src/server/client.h
@@ -3,6 +3,7 @@
 
 #include <signal.h>
 #include <time.h>
+#include <inttypes.h>
 
 /** CLIENT_HANDLER_TIMEOUT
  * This is the length of time (in seconds) any request can be outstanding for.
@@ -31,6 +32,8 @@ struct client {
 	int     fileno;
 	char*   mapped;
 
+	uint64_t  mapped_size;
+
 	struct self_pipe * stop_signal;
 
 	struct server* serve; /* FIXME: remove above duplication */