diff --git a/cores/c64/rtl/mos6526.v b/cores/c64/rtl/mos6526.v
index 66f5903..a51dc63 100644
--- a/cores/c64/rtl/mos6526.v
+++ b/cores/c64/rtl/mos6526.v
@@ -1,8 +1,7 @@
 // MOS6526
 // by Rayne
 // Timers & Interrupts are rewritten by slingshot
-// Passes all CIA Timer tests
-// TODO: check if Flag and Serial port interrupts are still working
+// Passes all Lorenz CIA Timer tests
 
 module mos6526 (
   input  wire       mode,   // 0 - 6526 "old", 1 - 8521 "new"
@@ -153,9 +152,14 @@ end
 
 // FLAG Input
 always @(posedge clk) begin
-  if (!res_n || int_reset) icr[4] <= 1'b0;
-  else if (!flag_n && flag_n_prev) icr[4] <= 1'b1;
-  if (phi2_p) flag_n_prev <= flag_n;
+  if (!res_n) icr[4] <= 1'b0;
+  else begin
+    if (!flag_n && flag_n_prev) icr[4] <= 1'b1;
+    if (phi2_p) begin
+      flag_n_prev <= flag_n;
+      if (int_reset) icr[4] <= 1'b0;
+    end
+  end
 end
 
 // Port Control Output