diff --git a/lib/northbound_oper.c b/lib/northbound_oper.c
index 6a3c21b237..bde2228012 100644
--- a/lib/northbound_oper.c
+++ b/lib/northbound_oper.c
@@ -1492,8 +1492,9 @@ static enum nb_error __walk(struct nb_op_yield_state *ys, bool is_resume)
 			 */
 			len = darr_strlen(ys->xpath);
 			if (ni->keys.num) {
-				yang_get_key_preds(ys->xpath + len, sib,
-						   &ni->keys,
+				darr_ensure_avail(ys->xpath,
+						  yang_get_key_pred_strlen(sib, &ni->keys) + 1);
+				yang_get_key_preds(ys->xpath + len, sib, &ni->keys,
 						   darr_cap(ys->xpath) - len);
 			} else {
 				/* add a position predicate (1s based?) */
diff --git a/lib/yang.c b/lib/yang.c
index dd48d8861b..0e2f78979a 100644
--- a/lib/yang.c
+++ b/lib/yang.c
@@ -1357,9 +1357,22 @@ uint32_t yang_get_list_elements_count(const struct lyd_node *node)
 	} while (node);
 	return count;
 }
+int yang_get_key_pred_strlen(const struct lysc_node *snode, const struct yang_list_keys *keys)
+{
+	const struct lysc_node_leaf *skey;
+	size_t len = 0;
+	size_t i = 0;
 
-int yang_get_key_preds(char *s, const struct lysc_node *snode,
-		       struct yang_list_keys *keys, ssize_t space)
+	LY_FOR_KEYS (snode, skey) {
+		/* [%s='%s'] */
+		len += 5 + strlen(skey->name) + strlen(keys->key[i]);
+		i++;
+	}
+	return len;
+}
+
+int yang_get_key_preds(char *s, const struct lysc_node *snode, const struct yang_list_keys *keys,
+		       ssize_t space)
 {
 	const struct lysc_node_leaf *skey;
 	ssize_t len2, len = 0;
diff --git a/lib/yang.h b/lib/yang.h
index 748f089037..afad0023ad 100644
--- a/lib/yang.h
+++ b/lib/yang.h
@@ -879,7 +879,11 @@ bool yang_is_last_level_dnode(const struct lyd_node *dnode);
 
 /* Create a YANG predicate string based on the keys */
 extern int yang_get_key_preds(char *s, const struct lysc_node *snode,
-			      struct yang_list_keys *keys, ssize_t space);
+			      const struct yang_list_keys *keys, ssize_t space);
+
+/* Get the length of the predicate string based on the keys */
+extern int yang_get_key_pred_strlen(const struct lysc_node *snode,
+				    const struct yang_list_keys *keys);
 
 /* Get YANG keys from an existing dnode */
 extern int yang_get_node_keys(struct lyd_node *node, struct yang_list_keys *keys);