diff --git a/src/core/net-sendbuffer.c b/src/core/net-sendbuffer.c
index dc951f3f..2c11fd4f 100644
--- a/src/core/net-sendbuffer.c
+++ b/src/core/net-sendbuffer.c
@@ -99,7 +99,7 @@ static int sig_sendbuffer(void)
 }
 
 /* Add `data' to transmit buffer - return FALSE if buffer is full */
-static int buffer_add(NET_SENDBUF_REC *rec, void *data, int size)
+static int buffer_add(NET_SENDBUF_REC *rec, const void *data, int size)
 {
 	if (rec->buffer == NULL) {
 		rec->buffer = g_malloc(rec->bufsize);
@@ -117,7 +117,7 @@ static int buffer_add(NET_SENDBUF_REC *rec, void *data, int size)
 /* Send data, if all of it couldn't be sent immediately, it will be resent
    automatically after a while. Returns -1 if some unrecoverable error
    occured. */
-int net_sendbuffer_send(NET_SENDBUF_REC *rec, void *data, int size)
+int net_sendbuffer_send(NET_SENDBUF_REC *rec, const void *data, int size)
 {
 	int ret;
 
diff --git a/src/core/net-sendbuffer.h b/src/core/net-sendbuffer.h
index 6b2ff372..848db9ec 100644
--- a/src/core/net-sendbuffer.h
+++ b/src/core/net-sendbuffer.h
@@ -14,7 +14,7 @@ void net_sendbuffer_destroy(NET_SENDBUF_REC *rec, int close);
 /* Send data, if all of it couldn't be sent immediately, it will be resent
    automatically after a while. Returns -1 if some unrecoverable error
    occured. */
-int net_sendbuffer_send(NET_SENDBUF_REC *rec, void *data, int size);
+int net_sendbuffer_send(NET_SENDBUF_REC *rec, const void *data, int size);
 
 /* Returns the socket handle */
 int net_sendbuffer_handle(NET_SENDBUF_REC *rec);