diff --git a/ports/MSP430/msp430_serial.c b/ports/MSP430/msp430_serial.c
index 26531ebbf..384cda0fc 100644
--- a/ports/MSP430/msp430_serial.c
+++ b/ports/MSP430/msp430_serial.c
@@ -74,9 +74,10 @@ interrupt(USART0RX_VECTOR) u0rxirq(void) {
  */
 static void OutNotify1(void) {
 
-  if (!(U0IE & UTXIE0))
+  if (!(U0IE & UTXIE0)) {
     U0TXBUF = (uint8_t)chFDDRequestDataI(&COM1);
-  U0IE |= UTXIE0;
+    U0IE |= UTXIE0;
+  }
 }
 
 /*
@@ -140,9 +141,10 @@ interrupt(USART1RX_VECTOR) u1rxirq(void) {
  */
 static void OutNotify2(void) {
 
-  if (!(U1IE & UTXIE1))
+  if (!(U1IE & UTXIE1)) {
     U1TXBUF = (uint8_t)chFDDRequestDataI(&COM2);
-  U1IE |= UTXIE1;
+    U1IE |= UTXIE1;
+  }
 }
 
 /*
diff --git a/readme.txt b/readme.txt
index f4d8b4499..6409d689d 100644
--- a/readme.txt
+++ b/readme.txt
@@ -74,6 +74,7 @@ Win32-MinGW            - ChibiOS/RT simulator and demo into a WIN32 process,
 *****************************************************************************
 
 *** 0.7.3 ***
+- Small optimization to the MSP430 serial driver.
 - Removed the performance spreadsheet (it was *very* old) and added a
   directory containing the test reports ./docs/reports.