diff --git a/hash_address.h b/hash_address.h
index 11b9f2a..ed3d55b 100644
--- a/hash_address.h
+++ b/hash_address.h
@@ -3,6 +3,10 @@
 
 #include <stdint.h>
 
+#define XMSS_ADDR_TYPE_OTS 0
+#define XMSS_ADDR_TYPE_LTREE 1
+#define XMSS_ADDR_TYPE_HASHTREE 2
+
 void set_layer_addr(uint32_t addr[8], uint32_t layer);
 
 void set_tree_addr(uint32_t addr[8], uint64_t tree);
diff --git a/xmss_commons.c b/xmss_commons.c
index 7a8c936..c207752 100644
--- a/xmss_commons.c
+++ b/xmss_commons.c
@@ -201,9 +201,9 @@ int xmss_core_sign_open(const xmss_params *params,
     uint32_t ltree_addr[8] = {0};
     uint32_t node_addr[8] = {0};
 
-    set_type(ots_addr, 0);
-    set_type(ltree_addr, 1);
-    set_type(node_addr, 2);
+    set_type(ots_addr, XMSS_ADDR_TYPE_OTS);
+    set_type(ltree_addr, XMSS_ADDR_TYPE_LTREE);
+    set_type(node_addr, XMSS_ADDR_TYPE_HASHTREE);
 
     *mlen = smlen - params->bytes;
 
@@ -264,9 +264,9 @@ int xmssmt_core_sign_open(const xmss_params *params,
     uint32_t ltree_addr[8] = {0};
     uint32_t node_addr[8] = {0};
 
-    set_type(ots_addr, 0);
-    set_type(ltree_addr, 1);
-    set_type(node_addr, 2);
+    set_type(ots_addr, XMSS_ADDR_TYPE_OTS);
+    set_type(ltree_addr, XMSS_ADDR_TYPE_LTREE);
+    set_type(node_addr, XMSS_ADDR_TYPE_HASHTREE);
 
     *mlen = smlen - params->bytes;
 
diff --git a/xmss_core.c b/xmss_core.c
index 4b17b1a..d996233 100644
--- a/xmss_core.c
+++ b/xmss_core.c
@@ -39,9 +39,9 @@ static void treehash(const xmss_params *params,
     copy_subtree_addr(ltree_addr, subtree_addr);
     copy_subtree_addr(node_addr, subtree_addr);
 
-    set_type(ots_addr, 0);
-    set_type(ltree_addr, 1);
-    set_type(node_addr, 2);
+    set_type(ots_addr, XMSS_ADDR_TYPE_OTS);
+    set_type(ltree_addr, XMSS_ADDR_TYPE_LTREE);
+    set_type(node_addr, XMSS_ADDR_TYPE_HASHTREE);
 
     for (idx = 0; idx < (uint32_t)(1 << params->tree_height); idx++) {
         /* Add the next leaf node to the stack. */
@@ -119,7 +119,7 @@ int xmss_core_sign(const xmss_params *params,
     unsigned char idx_bytes_32[32];
 
     uint32_t ots_addr[8] = {0};
-    set_type(ots_addr, 0);
+    set_type(ots_addr, XMSS_ADDR_TYPE_OTS);
 
     /* Read and use the current index from the secret key. */
     idx = (unsigned long)bytes_to_ull(sk, params->index_len);
@@ -212,7 +212,7 @@ int xmssmt_core_sign(const xmss_params *params,
     uint32_t idx_leaf;
 
     uint32_t ots_addr[8] = {0};
-    set_type(ots_addr, 0);
+    set_type(ots_addr, XMSS_ADDR_TYPE_OTS);
 
     /* Read and use the current index from the secret key. */
     idx = (unsigned long)bytes_to_ull(sk, params->index_len);
@@ -233,7 +233,7 @@ int xmssmt_core_sign(const xmss_params *params,
     hash_message(params, mhash, sm, pub_root, idx, m, mlen);
     sm += params->n;
 
-    set_type(ots_addr, 0);
+    set_type(ots_addr, XMSS_ADDR_TYPE_OTS);
 
     for (i = 0; i < params->d; i++) {
         idx_leaf = (idx & ((1 << params->tree_height)-1));