diff --git a/cores/arduino/SERCOM.cpp b/cores/arduino/SERCOM.cpp
index 42c46d015..200c6cda1 100644
--- a/cores/arduino/SERCOM.cpp
+++ b/cores/arduino/SERCOM.cpp
@@ -175,7 +175,7 @@ int SERCOM::writeDataUART(uint8_t data)
 
 void SERCOM::enableDataRegisterEmptyInterruptUART()
 {
-  sercom->USART.INTENSET.reg |= SERCOM_USART_INTENSET_DRE;
+  sercom->USART.INTENSET.reg = SERCOM_USART_INTENSET_DRE;
 }
 
 void SERCOM::disableDataRegisterEmptyInterruptUART()