diff --git a/test/sim/tb_cxxrtl/tb.v b/test/sim/tb_cxxrtl/tb.v
index 872fb12..d8bd58c 100644
--- a/test/sim/tb_cxxrtl/tb.v
+++ b/test/sim/tb_cxxrtl/tb.v
@@ -77,8 +77,13 @@ hazard3_reset_sync dmi_reset_sync_u (
 	.rst_n_out (rst_n_dmi)
 );
 
+// Note the idle hint of 8 cycles was empirically found to be the correct
+// value for a 1:2 TCK:clk_dmi ratio. OpenOCD doesn't particularly care
+// because it will just increase idle cycles until it stops seeing BUSY.
+
 hazard3_jtag_dtm #(
-	.IDCODE (IDCODE)
+	.IDCODE          (IDCODE),
+	.DTMCS_IDLE_HINT (8)
 ) inst_hazard3_jtag_dtm (
 	.tck              (tck),
 	.trst_n           (trst_n),
diff --git a/test/sim/tb_cxxrtl/tb_multicore.v b/test/sim/tb_cxxrtl/tb_multicore.v
index 38ba370..bc8197c 100644
--- a/test/sim/tb_cxxrtl/tb_multicore.v
+++ b/test/sim/tb_cxxrtl/tb_multicore.v
@@ -78,7 +78,8 @@ hazard3_reset_sync dmi_reset_sync_u (
 );
 
 hazard3_jtag_dtm #(
-	.IDCODE (IDCODE)
+	.IDCODE          (IDCODE),
+	.DTMCS_IDLE_HINT (8)
 ) inst_hazard3_jtag_dtm (
 	.tck              (tck),
 	.trst_n           (trst_n),