diff --git a/src/apps/tftp/tftp.c b/src/apps/tftp/tftp.c
index 46b7ae3a..3c175a6a 100644
--- a/src/apps/tftp/tftp.c
+++ b/src/apps/tftp/tftp.c
@@ -89,10 +89,10 @@ struct tftp_state {
   u16_t blknum;
   u8_t retries;
   u8_t mode_write;
+  u8_t tftp_mode;
 };
 
 static struct tftp_state tftp_state;
-static u8_t tftp_mode;
 
 static void tftp_tmr(void *arg);
 
@@ -117,12 +117,12 @@ close_handle(void)
 }
 
 static struct pbuf*
-init_packet(int opcode, int extra, int size)
+init_packet(u16_t opcode, u16_t extra, size_t size)
 {
   struct pbuf* p = pbuf_alloc(PBUF_TRANSPORT, (u16_t)(TFTP_HEADER_LENGTH + size), PBUF_RAM);
   u16_t* payload;
 
-  if(p != NULL) {
+  if (p != NULL) {
     payload = (u16_t*) p->payload;
     payload[0] = PP_HTONS(opcode);
     payload[1] = lwip_htons(extra);
@@ -131,74 +131,83 @@ init_packet(int opcode, int extra, int size)
   return p;
 }
 
-static void
-send_request(const ip_addr_t *addr, u16_t port, int opcode, const char* fname, const char* mode)
+static err_t
+send_request(const ip_addr_t *addr, u16_t port, u16_t opcode, const char* fname, const char* mode)
 {
   size_t fname_length = strlen(fname)+1;
   size_t mode_length = strlen(mode)+1;
-  struct pbuf* p = init_packet(opcode, 0, -2 + fname_length + mode_length);
+  struct pbuf* p = init_packet(opcode, 0, fname_length + mode_length - 2);
   char* payload;
+  err_t ret;
 
-  if(p == NULL) {
-    return;
+  if (p == NULL) {
+    return ERR_MEM;
   }
 
   payload = (char*) p->payload;
   MEMCPY(payload+2,              fname, fname_length);
   MEMCPY(payload+2+fname_length, mode,  mode_length);
 
-  udp_sendto(tftp_state.upcb, p, addr, port);
+  ret = udp_sendto(tftp_state.upcb, p, addr, port);
   pbuf_free(p);
+  return ret;
 }
 
-static void
+static err_t
 send_error(const ip_addr_t *addr, u16_t port, enum tftp_error code, const char *str)
 {
   int str_length = strlen(str);
   struct pbuf *p;
   u16_t *payload;
+  err_t ret;
 
   p = init_packet(TFTP_ERROR, code, str_length + 1);
   if (p == NULL) {
-    return;
+    return ERR_MEM;
   }
 
   payload = (u16_t *) p->payload;
   MEMCPY(&payload[2], str, str_length + 1);
 
-  udp_sendto(tftp_state.upcb, p, addr, port);
+  ret = udp_sendto(tftp_state.upcb, p, addr, port);
   pbuf_free(p);
+  return ret;
 }
 
-static void
+static err_t
 send_ack(const ip_addr_t *addr, u16_t port, u16_t blknum)
 {
   struct pbuf *p;
+  err_t ret;
 
   p = init_packet(TFTP_ACK, blknum, 0);
   if (p == NULL) {
-    return;
+    return ERR_MEM;
   }
 
-  udp_sendto(tftp_state.upcb, p, addr, port);
+  ret = udp_sendto(tftp_state.upcb, p, addr, port);
   pbuf_free(p);
+  return ret;
 }
 
-static void
+static err_t
 resend_data(const ip_addr_t *addr, u16_t port)
 {
+  err_t ret;
   struct pbuf *p = pbuf_alloc(PBUF_TRANSPORT, tftp_state.last_data->len, PBUF_RAM);
   if (p == NULL) {
-    return;
+    return ERR_MEM;
   }
 
-  if (pbuf_copy(p, tftp_state.last_data) != ERR_OK) {
+  ret = pbuf_copy(p, tftp_state.last_data);
+  if (ret != ERR_OK) {
     pbuf_free(p);
-    return;
+    return ret;
   }
 
-  udp_sendto(tftp_state.upcb, p, addr, port);
+  ret = udp_sendto(tftp_state.upcb, p, addr, port);
   pbuf_free(p);
+  return ret;
 }
 
 static void
@@ -264,7 +273,7 @@ recv(void *arg, struct udp_pcb *upcb, struct pbuf *p, const ip_addr_t *addr, u16
         break;
       }
 
-      if ((tftp_mode & LWIP_TFTP_MODE_SERVER) == 0) {
+      if ((tftp_state.tftp_mode & LWIP_TFTP_MODE_SERVER) == 0) {
         send_error(addr, port, TFTP_ERROR_ACCESS_VIOLATION, "TFTP server not enabled");
         break;
       }
@@ -444,8 +453,6 @@ tftp_init_common(u8_t mode, const struct tftp_context *ctx)
     return ERR_MEM;
   }
 
-  tftp_mode = mode;
-
   ret = udp_bind(pcb, IP_ANY_TYPE, TFTP_PORT);
   if (ret != ERR_OK) {
     udp_remove(pcb);
@@ -458,6 +465,7 @@ tftp_init_common(u8_t mode, const struct tftp_context *ctx)
   tftp_state.timer     = 0;
   tftp_state.last_data = NULL;
   tftp_state.upcb      = pcb;
+  tftp_state.tftp_mode = mode;
 
   udp_recv(pcb, recv, NULL);
 
@@ -498,25 +506,23 @@ void tftp_cleanup(void)
 err_t
 tftp_get(void* handle, const ip_addr_t *addr, u16_t port, const char* fname, const char* mode)
 {
-  LWIP_ERROR("TFTP client is not enabled (tftp_init)", (tftp_mode & LWIP_TFTP_MODE_CLIENT) == 0, return ERR_VAL);
+  LWIP_ERROR("TFTP client is not enabled (tftp_init)", (tftp_state.tftp_mode & LWIP_TFTP_MODE_CLIENT) != 0, return ERR_VAL);
 
   tftp_state.handle = handle;
   tftp_state.blknum = 1;
   tftp_state.mode_write = 1; /* We want to receive data */
-  send_request(addr, port, TFTP_RRQ, fname, mode);
-  return ERR_OK;
+  return send_request(addr, port, TFTP_RRQ, fname, mode);
 }
 
 err_t
 tftp_put(void* handle, const ip_addr_t *addr, u16_t port, const char* fname, const char* mode)
 {
-  LWIP_ERROR("TFTP client is not enabled (tftp_init)", (tftp_mode & LWIP_TFTP_MODE_CLIENT) == 0, return ERR_VAL);
+  LWIP_ERROR("TFTP client is not enabled (tftp_init)", (tftp_state.tftp_mode & LWIP_TFTP_MODE_CLIENT) != 0, return ERR_VAL);
 
   tftp_state.handle = handle;
   tftp_state.blknum = 1;
   tftp_state.mode_write = 0; /* We want to send data */
-  send_request(addr, port, TFTP_WRQ, fname, mode);
-  return ERR_OK;
+  return send_request(addr, port, TFTP_WRQ, fname, mode);
 }
 
 #endif /* LWIP_UDP */