diff --git a/lib/modem.js b/lib/modem.js
index f98ad4a..3be3937 100644
--- a/lib/modem.js
+++ b/lib/modem.js
@@ -189,6 +189,8 @@ async function registerSignalStrengthBackgroundQuery() {
 }
 
 async function sendSMS(destination, msg) {
+    if (typeof destination !== 'string' || typeof msg !== 'string' || !destination.trim() || !msg.trim()) return;
+
     await mutex.setLockWaitForCommand();
     logger.info('Sending message', { destination, msg });
 
diff --git a/lib/mutex.js b/lib/mutex.js
index cf255bd..677b525 100644
--- a/lib/mutex.js
+++ b/lib/mutex.js
@@ -36,7 +36,7 @@ function releaseLockWaitForCommand() {
         } catch (e) {
             //
         }
-    }, 1500);
+    }, 2000);
 }
 
 exports.setLockWaitForOK = setLockWaitForOK;