diff --git a/insns/insn_mul.py b/insns/insn_mul.py
index 7e7fedd..2e45dfd 100644
--- a/insns/insn_mul.py
+++ b/insns/insn_mul.py
@@ -67,8 +67,10 @@ class rvfi_insn_mul(Elaboratable):
         m.d.comb += misa_ok.eq(1)
 
         # MUL instruction
+        altops_bitmask = Signal(64)
+        m.d.comb += altops_bitmask.eq(0x2cdf52a55876063e)
         result = Signal(self.RISCV_FORMAL_XLEN)
-        m.d.comb += result.eq(self.rvfi_rs1_rdata * self.rvfi_rs2_rdata)
+        m.d.comb += result.eq((self.rvfi_rs1_rdata + self.rvfi_rs2_rdata) ^ altops_bitmask)
         m.d.comb += self.spec_valid.eq(self.rvfi_valid & (~insn_padding) & (insn_funct7 == 0b0000001) & (insn_funct3 == 0b000) & (insn_opcode == 0b0110011))
         m.d.comb += self.spec_rs1_addr.eq(insn_rs1)
         m.d.comb += self.spec_rs2_addr.eq(insn_rs2)