diff --git a/core/timer.c b/core/timer.c
index 1eb74e8..4e479f7 100644
--- a/core/timer.c
+++ b/core/timer.c
@@ -51,7 +51,7 @@ static void tmrEmulate(VB *sim, uint32_t clocks) {
         /* Do not decrement counter */
         if (
             !sim->tmr.t_enb ||
-            !sim->tmr.t_clk_sel && sim->tmr.tick20 != 0
+            (!sim->tmr.t_clk_sel && sim->tmr.tick20 != 0)
         ) continue;
 
         /* Advance to the next counter value */