diff --git a/src/modbus-private.h b/src/modbus-private.h
index e65269b..784a7f9 100644
--- a/src/modbus-private.h
+++ b/src/modbus-private.h
@@ -76,8 +76,8 @@ typedef struct _modbus_backend {
     int (*build_response_basis) (sft_t *sft, uint8_t *rsp);
     int (*prepare_response_tid) (const uint8_t *req, int *req_length);
     int (*send_msg_pre) (uint8_t *req, int req_length);
-    ssize_t (*send) (int s, const uint8_t *req, int req_length);
-    ssize_t (*recv) (int s, uint8_t *rsp, int rsp_length);
+    ssize_t (*send) (modbus_t *ctx, const uint8_t *req, int req_length);
+    ssize_t (*recv) (modbus_t *ctx, uint8_t *rsp, int rsp_length);
     int (*check_integrity) (modbus_t *ctx, uint8_t *msg,
                             const int msg_length);
     int (*connect) (modbus_t *ctx);
diff --git a/src/modbus-rtu.c b/src/modbus-rtu.c
index 443a907..34441a1 100644
--- a/src/modbus-rtu.c
+++ b/src/modbus-rtu.c
@@ -156,14 +156,14 @@ int _modbus_rtu_send_msg_pre(uint8_t *req, int req_length)
     return req_length;
 }
 
-ssize_t _modbus_rtu_send(int s, const uint8_t *req, int req_length)
+ssize_t _modbus_rtu_send(modbus_t *ctx, const uint8_t *req, int req_length)
 {
-    return write(s, req, req_length);
+    return write(ctx->s, req, req_length);
 }
 
-ssize_t _modbus_rtu_recv(int s, uint8_t *rsp, int rsp_length)
+ssize_t _modbus_rtu_recv(modbus_t *ctx, uint8_t *rsp, int rsp_length)
 {
-    return read(s, rsp, rsp_length);
+    return read(ctx->s, rsp, rsp_length);
 }
 
 /* The check_crc16 function shall return the message length if the CRC is
diff --git a/src/modbus-tcp.c b/src/modbus-tcp.c
index f206391..04af558 100644
--- a/src/modbus-tcp.c
+++ b/src/modbus-tcp.c
@@ -130,17 +130,17 @@ int _modbus_tcp_send_msg_pre(uint8_t *req, int req_length)
     return req_length;
 }
 
-ssize_t _modbus_tcp_send(int s, const uint8_t *req, int req_length)
+ssize_t _modbus_tcp_send(modbus_t *ctx, const uint8_t *req, int req_length)
 {
     /* MSG_NOSIGNAL
        Requests not to send SIGPIPE on errors on stream oriented
        sockets when the other end breaks the connection.  The EPIPE
        error is still returned. */
-    return send(s, req, req_length, MSG_NOSIGNAL);
+    return send(ctx->s, req, req_length, MSG_NOSIGNAL);
 }
 
-ssize_t _modbus_tcp_recv(int s, uint8_t *rsp, int rsp_length) {
-    return recv(s, rsp, rsp_length, 0);
+ssize_t _modbus_tcp_recv(modbus_t *ctx, uint8_t *rsp, int rsp_length) {
+    return recv(ctx->s, rsp, rsp_length, 0);
 }
 
 int _modbus_tcp_check_integrity(modbus_t *ctx, uint8_t *msg, const int msg_length)
diff --git a/src/modbus.c b/src/modbus.c
index 793acc6..df1f43b 100644
--- a/src/modbus.c
+++ b/src/modbus.c
@@ -156,7 +156,7 @@ static int send_msg(modbus_t *ctx, uint8_t *req, int req_length)
     /* In recovery mode, the write command will be issued until to be
        successful! Disabled by default. */
     do {
-        rc = ctx->backend->send(ctx->s, req, req_length);
+        rc = ctx->backend->send(ctx, req, req_length);
         if (rc == -1) {
             _error_print(ctx, NULL);
             if (ctx->error_recovery &&
@@ -346,7 +346,7 @@ static int receive_msg(modbus_t *ctx, int msg_length_computed,
 
     p_msg = msg;
     while (s_rc) {
-        read_rc = ctx->backend->recv(ctx->s, p_msg, length_to_read);
+        read_rc = ctx->backend->recv(ctx, p_msg, length_to_read);
         if (read_rc == 0) {
             errno = ECONNRESET;
             read_rc = -1;