diff --git a/armsrc/usart.c b/armsrc/usart.c
index f3abb40a1..2062c9441 100644
--- a/armsrc/usart.c
+++ b/armsrc/usart.c
@@ -49,7 +49,7 @@ static size_t us_rxfifo_high = 0;
 
 
 static void usart_fill_rxfifo(void) {
-    uint16_t rxfifo_free = 0;
+    uint16_t rxfifo_free ;
     if (pUS1->US_RNCR == 0) { // One buffer got filled, backup buffer being used
         if (us_rxfifo_low > us_rxfifo_high)
             rxfifo_free = us_rxfifo_low - us_rxfifo_high;