diff --git a/src/near_core/enc/asl1_core_codec.c b/src/near_core/enc/asl1_core_codec.c
index 8aac83a..0c892ee 100644
--- a/src/near_core/enc/asl1_core_codec.c
+++ b/src/near_core/enc/asl1_core_codec.c
@@ -192,6 +192,9 @@ bool amduat_enc_asl1_core_encode_reference_v1(
   if (reference.digest.len != 0 && reference.digest.data == NULL) {
     return false;
   }
+  if (reference.hash_id == 0u) {
+    return false;
+  }
 
   digest_len = reference.digest.len;
   hash_desc = amduat_hash_asl1_desc_lookup(reference.hash_id);
@@ -238,6 +241,9 @@ bool amduat_enc_asl1_core_decode_reference_v1(
   }
 
   hash_id = (amduat_hash_id_t)amduat_enc_asl1_core_load_u16_be(bytes.data);
+  if (hash_id == 0u) {
+    return false;
+  }
   digest_len = bytes.len - AMDUAT_ENC_ASL1_CORE_REF_HASH_LEN;
   hash_desc = amduat_hash_asl1_desc_lookup(hash_id);
   if (hash_desc != NULL && hash_desc->digest_len != 0 &&