diff --git a/mp_unpack.c b/mp_unpack.c
index f0127fa4..41e4cbde 100644
--- a/mp_unpack.c
+++ b/mp_unpack.c
@@ -13,6 +13,10 @@ mp_err mp_unpack(mp_int *rop, size_t count, mp_order order, size_t size,
    size_t odd_nails, nail_bytes, i, j;
    uint8_t odd_nail_mask;
 
+   if ((size == 0u) || (nails >= (size * 8u))) {
+      return MP_VAL;
+   }
+
    mp_zero(rop);
 
    if (endian == MP_NATIVE_ENDIAN) {