diff --git a/riscv/arith.h b/riscv/arith.h
index 7e471b2cb6..b61b28c4e3 100644
--- a/riscv/arith.h
+++ b/riscv/arith.h
@@ -40,7 +40,7 @@ inline int64_t mulhsu(int64_t a, uint64_t b)
 {
   int negate = a < 0;
   uint64_t res = mulhu(a < 0 ? -(uint64_t)a : a, b);
-  return negate ? ~res + (a * b == 0) : res;
+  return negate ? ~res + ((uint64_t)a * b == 0) : res;
 }
 
 //ref:  https://locklessinc.com/articles/sat_arithmetic/