diff --git a/target/sim/src/astral_fix.sv b/target/sim/src/astral_fix.sv
index e44e77b2..c674745f 100644
--- a/target/sim/src/astral_fix.sv
+++ b/target/sim/src/astral_fix.sv
@@ -840,7 +840,8 @@ module astral_fixture;
   ///////////////////////
 
   if (CarfieldIslandsCfg.safed.enable) begin : gen_safed_vip
-    localparam time ClkPeriodSafedJtag = ClkPeriodRef * 2;
+    // We assume 50 MHz for Safety Island JTAG
+    localparam time ClkPeriodSafedJtag = 20 ns;
 
     localparam axi_in_t AxiIn = gen_axi_in(DutCfg);
     localparam int unsigned AxiSlvIdWidth = DutCfg.AxiMstIdWidth + $clog2(AxiIn.num_in);
@@ -906,7 +907,8 @@ module astral_fixture;
   /////////////////////////
 
   if (CarfieldIslandsCfg.secured.enable) begin: gen_scured_vip
-    localparam time ClkPeriodSecdJtag = ClkPeriodJtag / 5;
+    // We assume 50 MHz for OpenTitan JTAG
+    localparam time ClkPeriodSecdJtag = 20 ns;
 
     // VIP
     vip_security_island_soc #(