diff --git a/kernel/arch/i386/system.c b/kernel/arch/i386/system.c
index 72d28b8b7..2f96901d8 100644
--- a/kernel/arch/i386/system.c
+++ b/kernel/arch/i386/system.c
@@ -89,7 +89,7 @@ PUBLIC void arch_stop_profile_clock(void)
   outb(RTC_INDEX, RTC_REG_B);
   r = inb(RTC_IO);
   outb(RTC_INDEX, RTC_REG_B);  
-  outb(RTC_IO, r & !RTC_B_PIE);
+  outb(RTC_IO, r & ~RTC_B_PIE);
 }
 
 PUBLIC void arch_ack_profile_clock(void)