diff --git a/NTPClient.cpp b/NTPClient.cpp
index 1f62f7f..127d412 100644
--- a/NTPClient.cpp
+++ b/NTPClient.cpp
@@ -26,7 +26,7 @@ void NTPClient::set_server(const char* server, int port) {
     nist_server_port = port;
 }
 
-time_t NTPClient::get_timestamp(int timeout) {
+int NTPClient::get_timestamp(time_t &timestamp, int timeout) {
     const time_t TIME1970 = (time_t)2208988800UL;
     int ntp_send_values[12] = {0};
     int ntp_recv_values[12] = {0};
@@ -58,8 +58,8 @@ time_t NTPClient::get_timestamp(int timeout) {
         const int n = sock.recvfrom(&source, (void*)ntp_recv_values, sizeof(ntp_recv_values));
 
         if (n > 10) {
-            return ntohl(ntp_recv_values[10]) - TIME1970;
-
+            timestamp = ntohl(ntp_recv_values[10]) - TIME1970;
+            return 0;
         } else {
             if (n < 0) {
                 // Network error
@@ -77,6 +77,18 @@ time_t NTPClient::get_timestamp(int timeout) {
     }
 }
 
+time_t NTPClient::get_timestamp(int timeout) {
+    time_t timestamp;
+    int ret = get_timestamp(timestamp, timeout);
+    if (ret < 0) {
+        // This doesn't work with the ARM toolchain whose time_t is unsigned
+        // Please use the new API get_timestamp(time_t *timestamp, int timeout)
+        return ret;
+    } else {
+        return timestamp;
+    }
+}
+
 void NTPClient::network(NetworkInterface *interface) {
     iface = interface;
 }
diff --git a/NTPClient.h b/NTPClient.h
index 8f755f5..84741ca 100644
--- a/NTPClient.h
+++ b/NTPClient.h
@@ -15,6 +15,7 @@
  */
 
 #include "mbed.h"
+#include "platform/mbed_toolchain.h"
 
 #define NTP_DEFULT_NIST_SERVER_ADDRESS "2.pool.ntp.org"
 #define NTP_DEFULT_NIST_SERVER_PORT 123
@@ -22,8 +23,16 @@
 class NTPClient {
     public:
         explicit NTPClient(NetworkInterface *interface = NULL);
+
         void set_server(const char* server, int port);
+
+        int get_timestamp(time_t &timestamp, int timeout = 15000);
+
+        MBED_DEPRECATED(
+            "This cannot return negative error codes with ARM toolchain's unsigned time_t. "
+            "Please use int get_timestamp(time_t &timestamp, int timeout) instead")
         time_t get_timestamp(int timeout = 15000);
+
         void network(NetworkInterface *interface);
 
     private: