diff --git a/src/modbus-rtu.c b/src/modbus-rtu.c
index 786a20b..64a297a 100644
--- a/src/modbus-rtu.c
+++ b/src/modbus-rtu.c
@@ -157,14 +157,14 @@ static uint16_t crc16(uint8_t *buffer, uint16_t buffer_length)
     return (crc_hi << 8 | crc_lo);
 }
 
-int _modbus_rtu_prepare_response_tid(const uint8_t *req, int *req_length)
+static int _modbus_rtu_prepare_response_tid(const uint8_t *req, int *req_length)
 {
     (*req_length) -= _MODBUS_RTU_CHECKSUM_LENGTH;
     /* No TID */
     return 0;
 }
 
-int _modbus_rtu_send_msg_pre(uint8_t *req, int req_length)
+static int _modbus_rtu_send_msg_pre(uint8_t *req, int req_length)
 {
     uint16_t crc = crc16(req, req_length);
     req[req_length++] = crc >> 8;
@@ -260,7 +260,7 @@ static int win32_ser_read(struct win32_ser *ws, uint8_t *p_msg,
 }
 #endif
 
-void _modbus_rtu_ioctl_rts(int fd, int on)
+static void _modbus_rtu_ioctl_rts(int fd, int on)
 {
 #if HAVE_DECL_TIOCM_RTS
     int flags;
@@ -275,7 +275,7 @@ void _modbus_rtu_ioctl_rts(int fd, int on)
 #endif
 }
 
-ssize_t _modbus_rtu_send(modbus_t *ctx, const uint8_t *req, int req_length)
+static ssize_t _modbus_rtu_send(modbus_t *ctx, const uint8_t *req, int req_length)
 {
 #if defined(_WIN32)
     modbus_rtu_t *ctx_rtu = ctx->backend_data;
@@ -309,7 +309,7 @@ ssize_t _modbus_rtu_send(modbus_t *ctx, const uint8_t *req, int req_length)
 #endif
 }
 
-int _modbus_rtu_receive(modbus_t *ctx, uint8_t *req)
+static int _modbus_rtu_receive(modbus_t *ctx, uint8_t *req)
 {
     int rc;
     modbus_rtu_t *ctx_rtu = ctx->backend_data;
@@ -332,7 +332,7 @@ int _modbus_rtu_receive(modbus_t *ctx, uint8_t *req)
     return rc;
 }
 
-ssize_t _modbus_rtu_recv(modbus_t *ctx, uint8_t *rsp, int rsp_length)
+static ssize_t _modbus_rtu_recv(modbus_t *ctx, uint8_t *rsp, int rsp_length)
 {
 #if defined(_WIN32)
     return win32_ser_read(&((modbus_rtu_t *)ctx->backend_data)->w_ser, rsp, rsp_length);
@@ -341,10 +341,10 @@ ssize_t _modbus_rtu_recv(modbus_t *ctx, uint8_t *rsp, int rsp_length)
 #endif
 }
 
-int _modbus_rtu_flush(modbus_t *);
+static int _modbus_rtu_flush(modbus_t *);
 
-int _modbus_rtu_pre_check_confirmation(modbus_t *ctx, const uint8_t *req,
-                                       const uint8_t *rsp, int rsp_length)
+static int _modbus_rtu_pre_check_confirmation(modbus_t *ctx, const uint8_t *req,
+                                              const uint8_t *rsp, int rsp_length)
 {
     /* Check responding slave is the slave we requested (except for broacast
      * request) */
@@ -364,8 +364,8 @@ int _modbus_rtu_pre_check_confirmation(modbus_t *ctx, const uint8_t *req,
 /* The check_crc16 function shall return 0 is the message is ignored and the
    message length if the CRC is valid. Otherwise it shall return -1 and set
    errno to EMBADCRC. */
-int _modbus_rtu_check_integrity(modbus_t *ctx, uint8_t *msg,
-                                const int msg_length)
+static int _modbus_rtu_check_integrity(modbus_t *ctx, uint8_t *msg,
+                                       const int msg_length)
 {
     uint16_t crc_calculated;
     uint16_t crc_received;
@@ -917,7 +917,7 @@ int modbus_rtu_get_rts(modbus_t *ctx) {
     }
 }
 
-void _modbus_rtu_close(modbus_t *ctx)
+static void _modbus_rtu_close(modbus_t *ctx)
 {
     /* Closes the file descriptor in RTU mode */
     modbus_rtu_t *ctx_rtu = ctx->backend_data;
@@ -937,7 +937,7 @@ void _modbus_rtu_close(modbus_t *ctx)
 #endif
 }
 
-int _modbus_rtu_flush(modbus_t *ctx)
+static int _modbus_rtu_flush(modbus_t *ctx)
 {
 #if defined(_WIN32)
     modbus_rtu_t *ctx_rtu = ctx->backend_data;
@@ -948,7 +948,7 @@ int _modbus_rtu_flush(modbus_t *ctx)
 #endif
 }
 
-int _modbus_rtu_select(modbus_t *ctx, fd_set *rset,
+static int _modbus_rtu_select(modbus_t *ctx, fd_set *rset,
                        struct timeval *tv, int length_to_read)
 {
     int s_rc;
@@ -987,7 +987,7 @@ int _modbus_rtu_select(modbus_t *ctx, fd_set *rset,
     return s_rc;
 }
 
-void _modbus_rtu_free(modbus_t *ctx) {
+static void _modbus_rtu_free(modbus_t *ctx) {
     free(((modbus_rtu_t*)ctx->backend_data)->device);
     free(ctx->backend_data);
     free(ctx);
diff --git a/src/modbus-tcp.c b/src/modbus-tcp.c
index 268c852..40a5eb5 100644
--- a/src/modbus-tcp.c
+++ b/src/modbus-tcp.c
@@ -16,8 +16,6 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-/* For accept4 when available */
-#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -97,9 +95,9 @@ static int _modbus_set_slave(modbus_t *ctx, int slave)
 }
 
 /* Builds a TCP request header */
-int _modbus_tcp_build_request_basis(modbus_t *ctx, int function,
-                                    int addr, int nb,
-                                    uint8_t *req)
+static int _modbus_tcp_build_request_basis(modbus_t *ctx, int function,
+                                           int addr, int nb,
+                                           uint8_t *req)
 {
     modbus_tcp_t *ctx_tcp = ctx->backend_data;
 
@@ -129,7 +127,7 @@ int _modbus_tcp_build_request_basis(modbus_t *ctx, int function,
 }
 
 /* Builds a TCP response header */
-int _modbus_tcp_build_response_basis(sft_t *sft, uint8_t *rsp)
+static int _modbus_tcp_build_response_basis(sft_t *sft, uint8_t *rsp)
 {
     /* Extract from MODBUS Messaging on TCP/IP Implementation
        Guide V1.0b (page 23/46):
@@ -152,12 +150,12 @@ int _modbus_tcp_build_response_basis(sft_t *sft, uint8_t *rsp)
 }
 
 
-int _modbus_tcp_prepare_response_tid(const uint8_t *req, int *req_length)
+static int _modbus_tcp_prepare_response_tid(const uint8_t *req, int *req_length)
 {
     return (req[0] << 8) + req[1];
 }
 
-int _modbus_tcp_send_msg_pre(uint8_t *req, int req_length)
+static int _modbus_tcp_send_msg_pre(uint8_t *req, int req_length)
 {
     /* Substract the header length to the message length */
     int mbap_length = req_length - 6;
@@ -168,7 +166,7 @@ int _modbus_tcp_send_msg_pre(uint8_t *req, int req_length)
     return req_length;
 }
 
-ssize_t _modbus_tcp_send(modbus_t *ctx, const uint8_t *req, int req_length)
+static 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
@@ -177,20 +175,20 @@ ssize_t _modbus_tcp_send(modbus_t *ctx, const uint8_t *req, int req_length)
     return send(ctx->s, (const char*)req, req_length, MSG_NOSIGNAL);
 }
 
-int _modbus_tcp_receive(modbus_t *ctx, uint8_t *req) {
+static int _modbus_tcp_receive(modbus_t *ctx, uint8_t *req) {
     return _modbus_receive_msg(ctx, req, MSG_INDICATION);
 }
 
-ssize_t _modbus_tcp_recv(modbus_t *ctx, uint8_t *rsp, int rsp_length) {
+static ssize_t _modbus_tcp_recv(modbus_t *ctx, uint8_t *rsp, int rsp_length) {
     return recv(ctx->s, (char *)rsp, rsp_length, 0);
 }
 
-int _modbus_tcp_check_integrity(modbus_t *ctx, uint8_t *msg, const int msg_length)
+static int _modbus_tcp_check_integrity(modbus_t *ctx, uint8_t *msg, const int msg_length)
 {
     return msg_length;
 }
 
-int _modbus_tcp_pre_check_confirmation(modbus_t *ctx, const uint8_t *req,
+static int _modbus_tcp_pre_check_confirmation(modbus_t *ctx, const uint8_t *req,
                                        const uint8_t *rsp, int rsp_length)
 {
     /* Check TID */
@@ -398,13 +396,13 @@ static int _modbus_tcp_pi_connect(modbus_t *ctx)
 }
 
 /* Closes the network connection and socket in TCP mode */
-void _modbus_tcp_close(modbus_t *ctx)
+static void _modbus_tcp_close(modbus_t *ctx)
 {
     shutdown(ctx->s, SHUT_RDWR);
     close(ctx->s);
 }
 
-int _modbus_tcp_flush(modbus_t *ctx)
+static int _modbus_tcp_flush(modbus_t *ctx)
 {
     int rc;
     int rc_sum = 0;
@@ -630,7 +628,7 @@ int modbus_tcp_pi_accept(modbus_t *ctx, int *socket)
     return ctx->s;
 }
 
-int _modbus_tcp_select(modbus_t *ctx, fd_set *rset, struct timeval *tv, int length_to_read)
+static int _modbus_tcp_select(modbus_t *ctx, fd_set *rset, struct timeval *tv, int length_to_read)
 {
     int s_rc;
     while ((s_rc = select(ctx->s+1, rset, NULL, NULL, tv)) == -1) {
@@ -654,7 +652,7 @@ int _modbus_tcp_select(modbus_t *ctx, fd_set *rset, struct timeval *tv, int leng
     return s_rc;
 }
 
-void _modbus_tcp_free(modbus_t *ctx) {
+static void _modbus_tcp_free(modbus_t *ctx) {
     free(ctx->backend_data);
     free(ctx);
 }
diff --git a/src/modbus.c b/src/modbus.c
index e887187..753d3a4 100644
--- a/src/modbus.c
+++ b/src/modbus.c
@@ -102,7 +102,7 @@ void _error_print(modbus_t *ctx, const char *context)
     }
 }
 
-int _sleep_and_flush(modbus_t *ctx)
+static int _sleep_and_flush(modbus_t *ctx)
 {
 #ifdef _WIN32
     /* usleep doesn't exist on Windows */
@@ -496,7 +496,7 @@ static int check_confirmation(modbus_t *ctx, uint8_t *req,
 
     /* Exception code */
     if (function >= 0x80) {
-        if (rsp_length == (offset + 2 + ctx->backend->checksum_length) &&
+        if (rsp_length == (offset + 2 + (int)ctx->backend->checksum_length) &&
             req[offset] == (rsp[offset] - 0x80)) {
             /* Valid exception code received */
 
diff --git a/tests/bandwidth-client.c b/tests/bandwidth-client.c
index d8dbc50..b4a173f 100644
--- a/tests/bandwidth-client.c
+++ b/tests/bandwidth-client.c
@@ -29,7 +29,7 @@
 
 #define G_MSEC_PER_SEC 1000
 
-uint32_t gettime_ms(void)
+static uint32_t gettime_ms(void)
 {
     struct timeval tv;
 #if !defined(_MSC_VER)