diff --git a/lib/CPUs/MIPS/syn/ise101/constraints/mips_top.xcf b/lib/CPUs/MIPS/syn/ise101/constraints/mips_top.xcf
index 5d908f7..1c877f4 100644
--- a/lib/CPUs/MIPS/syn/ise101/constraints/mips_top.xcf
+++ b/lib/CPUs/MIPS/syn/ise101/constraints/mips_top.xcf
@@ -1,3 +1,10 @@
+# Bus clock nets
+NET "CLK_I" TNM_NET = "sys_clk";
+TIMESPEC "TS_clk" = PERIOD "sys_clk" 9.9 ns HIGH 50 %;
+
+NET "cpu_clk" TNM_NET = "cpu_clk";
+TIMESPEC "TS_cpu_clk" = PERIOD "cpu_clk" 9.9 ns HIGH 50 %;
+
 BEGIN MODEL biu
 	INST inst_bin_fifo ram_style = distributed;
 	INST inst_bout_fifo ram_style = distributed;