diff --git a/hardware.hpp b/hardware.hpp
index 4cef107..4f8b7b8 100644
--- a/hardware.hpp
+++ b/hardware.hpp
@@ -376,9 +376,9 @@ class InterruptHardware {
   protected:
 	static void rxIntHandler() FORCE_INLINE
 	{
-		auto data = HardwareImpl::rxByteInterrupt();
+		const auto data = HardwareImpl::rxByteInterrupt();
 
-		uint8_t tmpHead = (sm_rxBuf.head + 1) % RX_BUFFER_SIZE;
+		const uint8_t tmpHead = (sm_rxBuf.head + 1) % RX_BUFFER_SIZE;
 
 		if (tmpHead != sm_rxBuf.tail) {
 			sm_rxBuf.head = tmpHead;
@@ -391,7 +391,7 @@ class InterruptHardware {
 	static void dataRegEmptyIntHandler() FORCE_INLINE
 	{
 		if (sm_txBuf.head != sm_txBuf.tail) {
-			uint8_t tmpTail = (sm_txBuf.tail + 1) % TX_BUFFER_SIZE;
+			const uint8_t tmpTail = (sm_txBuf.tail + 1) % TX_BUFFER_SIZE;
 			sm_txBuf.tail = tmpTail;
 			HardwareImpl::txByteInterrupt(sm_txBuf.buf[tmpTail]);
 		} else