diff --git a/I2CManager.h b/I2CManager.h
index 08d81d4..6a32853 100644
--- a/I2CManager.h
+++ b/I2CManager.h
@@ -1,6 +1,6 @@
 /*
  *  © 2023, Neil McKechnie. All rights reserved.
- *  © 2022 Paul M Antoine
+ *  © 2022-2024 Paul M Antoine
  *
  *  This file is part of CommandStation-EX
  *
@@ -519,14 +519,14 @@ private:
 
     // State is set to I2C_STATE_FREE when the interrupt handler has finished
     // the current request and is ready to complete.
-    uint8_t state = I2C_STATE_FREE;
+    uint8_t volatile state = I2C_STATE_FREE;
 
     // CompletionStatus may be set by the interrupt handler at any time but is
     // not written to the I2CRB until the state is I2C_STATE_FREE.
-    uint8_t completionStatus = I2C_STATUS_OK;
-    uint8_t overallStatus = I2C_STATUS_OK;
+    uint8_t volatile completionStatus = I2C_STATUS_OK;
+    uint8_t volatile overallStatus = I2C_STATUS_OK;
 
-    I2CRB * currentRequest = NULL;
+    I2CRB * volatile currentRequest = NULL;
     uint8_t txCount = 0;
     uint8_t rxCount = 0;
     uint8_t bytesToSend = 0;
diff --git a/I2CManager_NonBlocking.h b/I2CManager_NonBlocking.h
index 59bbcaf..6315915 100644
--- a/I2CManager_NonBlocking.h
+++ b/I2CManager_NonBlocking.h
@@ -1,6 +1,6 @@
 /*
  *  © 2023, Neil McKechnie
- *  © 2022 Paul M Antoine
+ *  © 2022-2024, Paul M Antoine
  *  All rights reserved.
  *
  *  This file is part of CommandStation-EX
@@ -245,8 +245,8 @@ void I2CManagerClass::checkForTimeout() {
     I2CRB *t = queueHead;
     if (state==I2C_STATE_ACTIVE && t!=0 && t==currentRequest && _timeout > 0) {
       // Check for timeout
-      int32_t elapsed = micros() - startTime;
-      if (elapsed > (int32_t)_timeout) { 
+      uint32_t elapsed = micros() - startTime;
+      if (elapsed > _timeout) { 
 #ifdef DIAG_IO
         //DIAG(F("I2CManager Timeout on %s"), t->i2cAddress.toString());
 #endif
diff --git a/I2CManager_STM32.h b/I2CManager_STM32.h
index cb6a03e..ea7152b 100644
--- a/I2CManager_STM32.h
+++ b/I2CManager_STM32.h
@@ -117,11 +117,11 @@ void I2CManagerClass::I2C_setClock(uint32_t i2cClockSpeed) {
   // while (s->CR1 & I2C_CR1_STOP);  // Prevents lockup by guarding further
   // writes to CR1 while STOP is being executed!
   // Should never happen, but wait for up to 500us only.
-  unsigned long startTime = micros();
+  uint32_t startTime = micros();
   bool timeout = false;
   while ((s->CR1 & I2C_CR1_STOP) != 0)
   {
-    if ((int32_t)(micros() - startTime) >= 500) {
+    if ((micros() - startTime) >= 500) {
       timeout = true;
       s->CR1 &= ~I2C_CR1_STOP; 
       break;