diff --git a/src/main.cpp b/src/main.cpp
index bdf6eca3..75187849 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -208,7 +208,9 @@ void lorawan_loop(void * pvParameters) {
 #endif
 
 void IRAM_ATTR ChannelSwitchIRQ() {
+    portENTER_CRITICAL(&timerMux);
     ChannelTimerIRQ++;
+    portEXIT_CRITICAL(&timerMux);
 }
 
 /* end hardware specific parts -------------------------------------------------------- */
diff --git a/src/main.h b/src/main.h
index 8b0d5b60..48390d7e 100644
--- a/src/main.h
+++ b/src/main.h
@@ -1,6 +1,6 @@
 
 // program version - note: increment version after modifications to configData_t struct!!
-#define PROGVERSION                     "1.3.3"    // use max 10 chars here!
+#define PROGVERSION                     "1.3.31"    // use max 10 chars here!
 #define PROGNAME                        "PAXCNT"
 
 //--- Declarations ---