diff --git a/src/NB_SMS.cpp b/src/NB_SMS.cpp
index 20c2025..6fce180 100644
--- a/src/NB_SMS.cpp
+++ b/src/NB_SMS.cpp
@@ -96,9 +96,7 @@ int NB_SMS::endSMS()
     MODEM.write(26);
 
     if (_synch) {
-      while ((r = MODEM.ready()) == 0) {
-        delay(100);
-      }
+      r = MODEM.waitForResponse(3*60*1000);
     } else {
       r = MODEM.ready();
     }
@@ -129,7 +127,8 @@ int NB_SMS::available()
     }
 
     if (_synch) {
-      while ((r = ready()) == 0) {
+      unsigned long start = millis();
+      while ((r = ready()) == 0 && (millis() - start) < 3*60*1000) {
         delay(100);
       }
     } else {