diff --git a/riscv/arith.h b/riscv/arith.h
index c60fcbea5f..7e471b2cb6 100644
--- a/riscv/arith.h
+++ b/riscv/arith.h
@@ -32,14 +32,14 @@ inline uint64_t mulhu(uint64_t a, uint64_t b)
 inline int64_t mulh(int64_t a, int64_t b)
 {
   int negate = (a < 0) != (b < 0);
-  uint64_t res = mulhu(a < 0 ? -a : a, b < 0 ? -b : b);
+  uint64_t res = mulhu(a < 0 ? -(uint64_t)a : a, b < 0 ? -(uint64_t)b : b);
   return negate ? ~res + ((uint64_t)a * (uint64_t)b == 0) : res;
 }
 
 inline int64_t mulhsu(int64_t a, uint64_t b)
 {
   int negate = a < 0;
-  uint64_t res = mulhu(a < 0 ? -a : a, b);
+  uint64_t res = mulhu(a < 0 ? -(uint64_t)a : a, b);
   return negate ? ~res + (a * b == 0) : res;
 }