--- src/kernel/sel4/src/plat/pc99/machine/io.c
+++ src/kernel/sel4/src/plat/pc99/machine/io.c
@@ -18,7 +18,7 @@
 
 void serial_init(uint16_t port)
 {
-    while (!(in8(port + 5) & 0x60)); /* wait until not busy */
+    while (!(in8(port + 5) & 0x20)); /* wait until not busy */
 
     out8(port + 1, 0x00); /* disable generating interrupts */
     out8(port + 3, 0x80); /* line control register: command: set divisor */
@@ -43,10 +43,10 @@ void console_putchar(char c)
     lock_acquire(&lock_debug);
 
     if (port > 0) {
-        while (!(in8(port + 5) & 0x60));
+        while (!(in8(port + 5) & 0x20));
         out8(port, c);
         if (c == '\n') {
-            while (!(in8(port + 5) & 0x60));
+            while (!(in8(port + 5) & 0x20));
             out8(port, '\r');
         }
     }