diff --git a/insns/insn_bltu.py b/insns/insn_bltu.py
index 58d60d2..36b6652 100644
--- a/insns/insn_bltu.py
+++ b/insns/insn_bltu.py
@@ -19,4 +19,12 @@ class rvfi_insn_bltu(rvfi_insn_SB_type):
         m.d.comb += self.spec_pc_wdata.eq(next_pc)
         m.d.comb += self.spec_trap.eq(Mux(self.ialign16, next_pc[0] != 0, next_pc[:2] != 0) | ~self.misa_ok)
 
+        # default assignments
+        m.d.comb += self.spec_rd_addr.eq(0)
+        m.d.comb += self.spec_rd_wdata.eq(0)
+        m.d.comb += self.spec_mem_addr.eq(0)
+        m.d.comb += self.spec_mem_rmask.eq(0)
+        m.d.comb += self.spec_mem_wmask.eq(0)
+        m.d.comb += self.spec_mem_wdata.eq(0)
+
         return m