diff --git a/programs/ssl/ssl_mail_client.c b/programs/ssl/ssl_mail_client.c
index 31da2ed..f755158 100644
--- a/programs/ssl/ssl_mail_client.c
+++ b/programs/ssl/ssl_mail_client.c
@@ -723,7 +723,7 @@
     mbedtls_printf("  > Write MAIL FROM to server:");
     fflush(stdout);
 
-    len = sprintf((char *) buf, "MAIL FROM:<%s>\r\n", opt.mail_from);
+    len = snprintf((char *) buf, sizeof(buf), "MAIL FROM:<%s>\r\n", opt.mail_from);
     ret = write_ssl_and_get_response(&ssl, buf, len);
     if (ret < 200 || ret > 299) {
         mbedtls_printf(" failed\n  ! server responded with %d\n\n", ret);
@@ -735,7 +735,7 @@
     mbedtls_printf("  > Write RCPT TO to server:");
     fflush(stdout);
 
-    len = sprintf((char *) buf, "RCPT TO:<%s>\r\n", opt.mail_to);
+    len = snprintf((char *) buf, sizeof(buf), "RCPT TO:<%s>\r\n", opt.mail_to);
     ret = write_ssl_and_get_response(&ssl, buf, len);
     if (ret < 200 || ret > 299) {
         mbedtls_printf(" failed\n  ! server responded with %d\n\n", ret);
@@ -759,11 +759,12 @@
     mbedtls_printf("  > Write content to server:");
     fflush(stdout);
 
-    len = sprintf((char *) buf, "From: %s\r\nSubject: Mbed TLS Test mail\r\n\r\n"
-                                "This is a simple test mail from the "
-                                "Mbed TLS mail client example.\r\n"
-                                "\r\n"
-                                "Enjoy!", opt.mail_from);
+    len = snprintf((char *) buf, sizeof(buf),
+                   "From: %s\r\nSubject: Mbed TLS Test mail\r\n\r\n"
+                   "This is a simple test mail from the "
+                   "Mbed TLS mail client example.\r\n"
+                   "\r\n"
+                   "Enjoy!", opt.mail_from);
     ret = write_ssl_data(&ssl, buf, len);
 
     len = sprintf((char *) buf, "\r\n.\r\n");