diff --git a/common/IO/Z80CTC/ctc_counter.vhd b/common/IO/Z80CTC/ctc_counter.vhd
index 58409ca2..da17d608 100644
--- a/common/IO/Z80CTC/ctc_counter.vhd
+++ b/common/IO/Z80CTC/ctc_counter.vhd
@@ -118,7 +118,7 @@ begin
 								time_constant_loaded <= '0';
 								zc_to_in <= '0';
 --								zc_to_in_r <= '0';
-								clk_trg_r <= clk_trg;
+								clk_trg_r <= clk_trg xor d_in(4);
 							end if;
 						end if;