diff --git a/rtl/ibex_multdiv_fast.sv b/rtl/ibex_multdiv_fast.sv
index 1e4026b9..ed1fc130 100644
--- a/rtl/ibex_multdiv_fast.sv
+++ b/rtl/ibex_multdiv_fast.sv
@@ -118,6 +118,10 @@ module ibex_multdiv_fast (
 
   assign multdiv_result_o = div_en_i ? mac_res_q[31:0] : mac_res_n[31:0];
 
+  // The 2 MSBs of mac_res_ext (mac_res_ext[34:33]) are always equal since:
+  // 1. The 2 MSBs of the multiplicants are always equal, and
+  // 2. The 16 MSBs of the addend (accum[33:18]) are always equal.
+  // Thus, it is safe to ignore mac_res_ext[34].
   assign mac_res_signed = $signed({sign_a, mult_op_a})*$signed({sign_b, mult_op_b}) + $signed(accum);
   assign mac_res_ext    = $unsigned(mac_res_signed);
   assign mac_res        = mac_res_ext[33:0];