diff --git a/ESPGeiger/src/Counter/Counter.cpp b/ESPGeiger/src/Counter/Counter.cpp
index 98623b2..3572702 100644
--- a/ESPGeiger/src/Counter/Counter.cpp
+++ b/ESPGeiger/src/Counter/Counter.cpp
@@ -138,10 +138,16 @@ void Counter::handleSerial(char* input)
     if (n == 1) {
 #endif
       Log::debug(PSTR("Counter loop - %d"), _scpm);
+#ifdef ESP32
+    portENTER_CRITICAL(&timerMux);
+#endif
 #if GEIGER_SERIAL_TYPE == GEIGER_SERIAL_CPM
       eventCounter = (float)_scpm/(float)60;
 #else
       eventCounter = (float)_scpm;
+#endif
+#ifdef ESP32
+    portEXIT_CRITICAL(&timerMux);
 #endif
     }
 }