diff --git a/hardware0.hpp b/hardware0.hpp
index 2ca13aa..cf733ca 100644
--- a/hardware0.hpp
+++ b/hardware0.hpp
@@ -2,6 +2,7 @@
 
 #include <stdint.h>
 
+#include <avr/interrupt.h>
 #include <avr/io.h>
 
 #include "config.hpp"
@@ -131,6 +132,7 @@ class Hardware0<mode, cfg, Driven::INTERRUPT> {
 		detail::fnDataReg0EmptyIntHandler = dataRegEmptyIntHandler;
 
 		HardwareImpl::init();
+		sei();
 	}
 
 	static void txByte(const data_t &byte) FORCE_INLINE
diff --git a/hardware1.hpp b/hardware1.hpp
index 185b24f..256b596 100644
--- a/hardware1.hpp
+++ b/hardware1.hpp
@@ -2,6 +2,7 @@
 
 #include <stdint.h>
 
+#include <avr/interrupt.h>
 #include <avr/io.h>
 
 #include "config.hpp"
@@ -135,6 +136,7 @@ class Hardware1<mode, cfg, Driven::INTERRUPT> {
 		detail::fnDataReg1EmptyIntHandler = dataRegEmptyIntHandler;
 
 		HardwareImpl::init();
+		sei();
 	}
 
 	static void txByte(const data_t &byte) FORCE_INLINE