diff --git a/hash.c b/hash.c
index 6f5eaff..0f9aa23 100644
--- a/hash.c
+++ b/hash.c
@@ -38,7 +38,7 @@ static int core_hash(const xmss_params *params,
         shake256(out, 64, in, inlen);
     }
     else {
-        return 1;
+        return -1;
     }
     return 0;
 }
diff --git a/params.c b/params.c
index 0a721a8..1ac7211 100644
--- a/params.c
+++ b/params.c
@@ -174,7 +174,7 @@ int xmss_parse_oid(xmss_params *params, const uint32_t oid)
             break;
 
         default:
-            return 1;
+            return -1;
     }
     switch (oid) {
         case 0x01000001:
@@ -198,7 +198,7 @@ int xmss_parse_oid(xmss_params *params, const uint32_t oid)
             break;
 
         default:
-            return 1;
+            return -1;
     }
     switch (oid) {
         case 0x01000001:
@@ -223,7 +223,7 @@ int xmss_parse_oid(xmss_params *params, const uint32_t oid)
 
             break;
         default:
-            return 1;
+            return -1;
     }
     params->d = 1;
     params->tree_height = params->full_height  / params->d;
@@ -289,7 +289,7 @@ int xmssmt_parse_oid(xmss_params *params, const uint32_t oid)
             break;
 
         default:
-            return 1;
+            return -1;
     }
     switch (oid) {
         case 0x01000001:
@@ -333,7 +333,7 @@ int xmssmt_parse_oid(xmss_params *params, const uint32_t oid)
             break;
 
         default:
-            return 1;
+            return -1;
     }
     switch (oid) {
         case 0x01000001:
@@ -387,7 +387,7 @@ int xmssmt_parse_oid(xmss_params *params, const uint32_t oid)
             break;
 
         default:
-            return 1;
+            return -1;
     }
     switch (oid) {
         case 0x01000001:
@@ -441,7 +441,7 @@ int xmssmt_parse_oid(xmss_params *params, const uint32_t oid)
             break;
 
         default:
-            return 1;
+            return -1;
     }
 
     params->tree_height = params->full_height  / params->d;
diff --git a/params.h b/params.h
index 48478c7..3cc76bd 100644
--- a/params.h
+++ b/params.h
@@ -33,26 +33,26 @@ typedef struct {
 /**
  * Accepts strings such as "XMSS-SHA2_10_256"
  *  and outputs OIDs such as 0x01000001.
- * Returns 1 when the parameter set is not found, 0 otherwise
+ * Returns -1 when the parameter set is not found, 0 otherwise
  */
 int xmss_str_to_oid(uint32_t *oid, const char* s);
 
 /**
  * Accepts takes strings such as "XMSSMT-SHA2_20/2_256"
  *  and outputs OIDs such as 0x01000001.
- * Returns 1 when the parameter set is not found, 0 otherwise
+ * Returns -1 when the parameter set is not found, 0 otherwise
  */
 int xmssmt_str_to_oid(uint32_t *oid, const char* s);
 
 /**
  * Accepts OIDs such as 0x01000001, and configures params accordingly.
- * Returns 1 when the OID is not found, 0 otherwise.
+ * Returns -1 when the OID is not found, 0 otherwise.
  */
 int xmss_parse_oid(xmss_params *params, const uint32_t oid);
 
 /**
  * Accepts OIDs such as 0x01000001, and configures params accordingly.
- * Returns 1 when the OID is not found, 0 otherwise.
+ * Returns -1 when the OID is not found, 0 otherwise.
  */
 int xmssmt_parse_oid(xmss_params *params, const uint32_t oid);
 
diff --git a/xmss.c b/xmss.c
index 7b9253a..0638f3e 100644
--- a/xmss.c
+++ b/xmss.c
@@ -13,7 +13,7 @@ int xmss_keypair(unsigned char *pk, unsigned char *sk, const uint32_t oid)
     unsigned int i;
 
     if (xmss_parse_oid(&params, oid)) {
-        return 1;
+        return -1;
     }
     for (i = 0; i < XMSS_OID_LEN; i++) {
         pk[i] = (oid >> (8 * i)) & 0xFF;
@@ -37,7 +37,7 @@ int xmss_sign(unsigned char *sk,
         oid |= sk[i] << (i * 8);
     }
     if (xmss_parse_oid(&params, oid)) {
-        return 1;
+        return -1;
     }
     return xmss_core_sign(&params, sk + XMSS_OID_LEN, sm, smlen, m, mlen);
 }
@@ -54,7 +54,7 @@ int xmss_sign_open(unsigned char *m, unsigned long long *mlen,
         oid |= pk[i] << (i * 8);
     }
     if (xmss_parse_oid(&params, oid)) {
-        return 1;
+        return -1;
     }
     return xmss_core_sign_open(&params, m, mlen, sm, smlen, pk + XMSS_OID_LEN);
 }
@@ -65,7 +65,7 @@ int xmssmt_keypair(unsigned char *pk, unsigned char *sk, const uint32_t oid)
     unsigned int i;
 
     if (xmssmt_parse_oid(&params, oid)) {
-        return 1;
+        return -1;
     }
     for (i = 0; i < XMSS_OID_LEN; i++) {
         pk[i] = (oid >> (8 * i)) & 0xFF;
@@ -86,7 +86,7 @@ int xmssmt_sign(unsigned char *sk,
         oid |= sk[i] << (i * 8);
     }
     if (xmssmt_parse_oid(&params, oid)) {
-        return 1;
+        return -1;
     }
     return xmssmt_core_sign(&params, sk + XMSS_OID_LEN, sm, smlen, m, mlen);
 }
@@ -103,7 +103,7 @@ int xmssmt_sign_open(unsigned char *m, unsigned long long *mlen,
         oid |= pk[i] << (i * 8);
     }
     if (xmssmt_parse_oid(&params, oid)) {
-        return 1;
+        return -1;
     }
     return xmssmt_core_sign_open(&params, m, mlen, sm, smlen, pk + XMSS_OID_LEN);
 }
diff --git a/xmss_core_fast.c b/xmss_core_fast.c
index 3d74527..e56ead3 100644
--- a/xmss_core_fast.c
+++ b/xmss_core_fast.c
@@ -328,8 +328,8 @@ static void treehash_update(const xmss_params *params,
 }
 
 /**
- * Performs one treehash update on the instance that needs it the most.
- * Returns 1 if such an instance was not found
+ * Performs treehash updates on the instance that needs it the most.
+ * Returns the updated number of available updates.
  **/
 static char bds_treehash_update(const xmss_params *params,
                                 bds_state *state, unsigned int updates,
@@ -370,7 +370,7 @@ static char bds_treehash_update(const xmss_params *params,
 
 /**
  * Updates the state (typically NEXT_i) by adding a leaf and updating the stack
- * Returns 1 if all leaf nodes have already been processed
+ * Returns -1 if all leaf nodes have already been processed
  **/
 static char bds_state_update(const xmss_params *params,
                              bds_state *state, const unsigned char *sk_seed,
@@ -384,7 +384,7 @@ static char bds_state_update(const xmss_params *params,
     unsigned int nodeh;
     int idx = state->next_leaf;
     if (idx == 1 << params->tree_height) {
-        return 1;
+        return -1;
     }
 
     // only copy layer and tree address parts