diff --git a/vsim/Makefrag b/vsim/Makefrag
index 2a129ee8..f4bcb7a5 100644
--- a/vsim/Makefrag
+++ b/vsim/Makefrag
@@ -39,7 +39,7 @@ VCS_OPTS = -notice -line +lint=all,noVCDE,noONGS,noUI -error=PCWM-L -timescale=1
 	$(RISCV)/lib/libfesvr.so \
 	-sverilog \
 	+incdir+$(generated_dir) \
-	+define+CLOCK_PERIOD=0.5 $(sim_vsrcs) $(sim_csrcs) \
+	+define+CLOCK_PERIOD=1.0 $(sim_vsrcs) $(sim_csrcs) \
 	+define+PRINTF_COND=$(TB).printf_cond \
 	+define+STOP_COND=!$(TB).reset \
 	+define+RANDOMIZE \
diff --git a/vsrc/TestDriver.v b/vsrc/TestDriver.v
index 92d61812..8ddcb22c 100644
--- a/vsrc/TestDriver.v
+++ b/vsrc/TestDriver.v
@@ -5,7 +5,7 @@ module TestDriver;
   reg clk   = 1'b0;
   reg reset = 1'b1;
 
-  always #`CLOCK_PERIOD clk = ~clk;
+  always #(`CLOCK_PERIOD/2.0) clk = ~clk;
   initial #777.7 reset = 0;
 
   // Read input arguments and initialize