diff --git a/modules/vector-sets/hnsw.c b/modules/vector-sets/hnsw.c
index cd38e4454..701c1f0d2 100644
--- a/modules/vector-sets/hnsw.c
+++ b/modules/vector-sets/hnsw.c
@@ -2058,6 +2058,18 @@ hnswNode *hnsw_random_node(HNSW *index, int slot) {
  * hash table, then scan all the nodes again and fix all the links converting
  * the ID to the pointer. */
 
+/* History of serialization versions:
+ * version 0: the first implementation, lacking worst node id/info.
+ * version 1: includes worst link id/info. */
+#define HNSW_SERIALIZATION_VERSION 1
+
+/* This is a special worst link index that is set when loading a serialized
+ * node with version 0 (this version of the serialization lacked explicit
+ * information about the worst link index/distance). This way, later, the
+ * function that fixes a deserialized index will know to compute the worst
+ * index info at runtime. */
+#define HNSW_SER_WORSTLINK_MISSING UINT32_MAX
+
 /* Return the serialized node information as specified in the top comment
  * above. Note that the returned information is true as long as the node
  * provided is not deleted or modified, so this function should be called
@@ -2073,6 +2085,7 @@ hnswSerNode *hnsw_serialize_node(HNSW *index, hnswNode *node) {
     for (uint32_t i = 0; i <= node->level; i++) {
         num_params += 2; // max_links and num_links info for this layer.
         num_params += node->layers[i].num_links; // The IDs of linked nodes.
+        num_params += 1; // worst link id/distance parameter.
     }
 
     /* We use another 64bit value to store two floats that are about
@@ -2096,18 +2109,43 @@ hnswSerNode *hnsw_serialize_node(HNSW *index, hnswNode *node) {
 
     uint32_t param_idx = 0;
     sn->params[param_idx++] = node->id;
-    sn->params[param_idx++] = node->level;
+    /* The second parameter contains information about the serialization
+     * version of this node, the node level and some unused field:
+     *
+     * +--------+--------+--------+--------+
+     * |VVVVVVVV|........|........|LLLLLLLL|
+     * +--------+--------+--------+--------+
+     *
+     * V is the version, 8 bits.
+     * L is the node level, 8 bits (but actually 16 is the max so far).
+     * The middle two bytes are reserved for future uses. */
+    sn->params[param_idx] = node->level & 0xff;
+    sn->params[param_idx] |= HNSW_SERIALIZATION_VERSION << 24;
+    param_idx++;
     for (uint32_t i = 0; i <= node->level; i++) {
         sn->params[param_idx++] = node->layers[i].num_links;
         sn->params[param_idx++] = node->layers[i].max_links;
         for (uint32_t j = 0; j < node->layers[i].num_links; j++) {
             sn->params[param_idx++] = node->layers[i].links[j]->id;
         }
+        /* Since version 1: pack and store worst_idx and worst_distance. */
+        uint32_t worst_distance_bits;
+        memcpy(&worst_distance_bits, &node->layers[i].worst_distance,
+               sizeof(float));
+        uint64_t wi =
+            (((uint64_t)worst_distance_bits) << 32) | node->layers[i].worst_idx;
+        sn->params[param_idx++] = wi;
     }
-    uint64_t l2_and_range = 0;
-    unsigned char *aux = (unsigned char*)&l2_and_range;
-    memcpy(aux,&node->l2,sizeof(float));
-    memcpy(aux+4,&node->quants_range,sizeof(float));
+
+    /* Store l2 and range as uint32_t, in a way that is endian-safe.
+     * Note that in big endian archs both are reversed: integers and
+     * also the bytes of floats, so they will match. */
+    uint64_t l2_and_range;
+    uint32_t l2_bits, range_bits;
+    memcpy(&l2_bits,&node->l2,sizeof(float));
+    memcpy(&range_bits,&node->quants_range,sizeof(float));
+    l2_and_range = ((uint64_t)range_bits<<32) | l2_bits;
+
     sn->params[param_idx++] = l2_and_range;
 
     /* Better safe than sorry: */
@@ -2128,13 +2166,18 @@ void hnsw_free_serialized_node(hnswSerNode *sn) {
  * The function returns NULL both on out of memory and if the remaining
  * parameters length does not match the number of links or other items
  * to load. */
-#define HNSW_SER_WORSTLINK_MISSING UINT32_MAX
 hnswNode *hnsw_insert_serialized(HNSW *index, void *vector, uint64_t *params, uint32_t params_len, void *value)
 {
     if (params_len < 2) return NULL;
 
     uint64_t id = params[0];
-    uint32_t level = params[1];
+    /* Check the node serialization function for the specific layout
+     * of param[1] fields. */
+    uint32_t level = params[1] & 0xff;                  // Node level.
+    uint32_t version = (params[1] & 0xff000000) >> 24;  // Format version.
+
+    if (version > HNSW_SERIALIZATION_VERSION) return NULL;
+    int has_worst_link_info = version > 0;
 
     /* Keep track of maximum ID seen while loading. */
     if (id >= index->last_id) index->last_id = id;
@@ -2152,7 +2195,7 @@ hnswNode *hnsw_insert_serialized(HNSW *index, void *vector, uint64_t *params, ui
     uint32_t param_idx = 2;
     for (uint32_t i = 0; i <= level; i++) {
         /* Sanity check. */
-        if (param_idx + 2 > params_len) {
+        if (param_idx + 2 + has_worst_link_info > params_len) {
             hnsw_node_free(node);
             return NULL;
         }
@@ -2183,7 +2226,7 @@ hnswNode *hnsw_insert_serialized(HNSW *index, void *vector, uint64_t *params, ui
         node->layers[i].num_links = num_links;
 
         /* Sanity check. */
-        if (param_idx + num_links > params_len) {
+        if (param_idx + num_links + has_worst_link_info > params_len) {
             hnsw_node_free(node);
             return NULL;
         }
@@ -2195,9 +2238,26 @@ hnswNode *hnsw_insert_serialized(HNSW *index, void *vector, uint64_t *params, ui
         for (uint32_t j = 0; j < num_links; j++)
             node->layers[i].links[j] = (hnswNode*)params[param_idx++];
 
-        /* XXX: fix me, we need to store the worst link info in a
-         * backward compatible way. */
-        node->layers[i].worst_idx = HNSW_SER_WORSTLINK_MISSING;
+        if (has_worst_link_info) {
+            uint64_t wi = params[param_idx++];
+            uint32_t worst_idx = wi & 0xffffffff;
+            uint32_t worst_distance_bits = wi >> 32;
+            float worst_distance;
+            memcpy(&worst_distance,&worst_distance_bits,sizeof(float));
+            node->layers[i].worst_idx = worst_idx;
+            node->layers[i].worst_distance = worst_distance;
+
+            // Sanity check the worst ID range.
+            if (node->layers[i].num_links > 0 &&
+                node->layers[i].worst_idx >= node->layers[i].num_links)
+            {
+                hnsw_node_free(node);
+                return NULL;
+            }
+        } else {
+            node->layers[i].worst_idx = HNSW_SER_WORSTLINK_MISSING;
+            node->layers[i].worst_distance = 0;
+        }
     }
 
     /* Get l2 and quantization range. */
@@ -2205,10 +2265,14 @@ hnswNode *hnsw_insert_serialized(HNSW *index, void *vector, uint64_t *params, ui
         hnsw_node_free(node);
         return NULL;
     }
+
+    /* Load l2 and range packed into an uint64_t in an endian safe way. */
     uint64_t l2_and_range = params[param_idx];
-    unsigned char *aux = (unsigned char*)&l2_and_range;
-    memcpy(&node->l2, aux, sizeof(float));
-    memcpy(&node->quants_range, aux+4, sizeof(float));
+    uint32_t l2_bits, range_bits;
+    l2_bits = l2_and_range & 0xffffffff;
+    range_bits = l2_and_range >> 32;
+    memcpy(&node->l2, &l2_bits, sizeof(float));
+    memcpy(&node->quants_range, &range_bits, sizeof(float));
 
     node->value = value;
     hnsw_add_node(index, node);