diff --git a/CHANGELOG.md b/CHANGELOG.md
index ef5b3138..aa21c781 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -32,8 +32,16 @@ NOTE: Add new changes BELOW THIS COMMENT.
 - Private rDNS resolution now also affects `SOA` and `NS` requests ([#6882]).
 - Rewrite rules mechanics was changed due to improve resolving in safe search.
 
+### Deprecated
+
+- Currently, AdGuard Home skips persistent clients that have duplicate fields
+  when reading them from the configuration file.  This behaviour is deprecated
+  and will cause errors on startup in a future release.
+
 ### Fixed
 
+- Acceptance of duplicate UIDs for persistent clients at startup.  See also the
+  section on client settings on the [Wiki page][wiki-config].
 - Domain specifications for top-level domains not considered for requests to
   unqualified domains ([#6744]).
 - Support for link-local subnets, i.e. `fe80::/16`, as client identifiers
diff --git a/internal/client/index.go b/internal/client/index.go
index 24ec6e30..18f826de 100644
--- a/internal/client/index.go
+++ b/internal/client/index.go
@@ -6,6 +6,7 @@ import (
 	"net/netip"
 
 	"github.com/AdguardTeam/AdGuardHome/internal/aghalg"
+	"github.com/AdguardTeam/golibs/errors"
 )
 
 // macKey contains MAC as byte array of 6, 8, or 20 bytes.
@@ -82,15 +83,25 @@ func (ci *Index) Add(c *Persistent) {
 	ci.uidToClient[c.UID] = c
 }
 
+// ErrDuplicateUID is an error returned by [Index.Clashes] when adding a
+// persistent client with a UID that already exists in an index.
+const ErrDuplicateUID errors.Error = "duplicate uid"
+
 // Clashes returns an error if the index contains a different persistent client
 // with at least a single identifier contained by c.  c must be non-nil.
 func (ci *Index) Clashes(c *Persistent) (err error) {
+	_, ok := ci.uidToClient[c.UID]
+	if ok {
+		return ErrDuplicateUID
+	}
+
 	for _, id := range c.ClientIDs {
-		existing, ok := ci.clientIDToUID[id]
+		var existing UID
+		existing, ok = ci.clientIDToUID[id]
 		if ok && existing != c.UID {
 			p := ci.uidToClient[existing]
 
-			return fmt.Errorf("another client %q uses the same ID %q", p.Name, id)
+			return fmt.Errorf("another client %q uses the same ClientID %q", p.Name, id)
 		}
 	}
 
diff --git a/internal/home/clients.go b/internal/home/clients.go
index 7a2487ca..9cc210ab 100644
--- a/internal/home/clients.go
+++ b/internal/home/clients.go
@@ -286,7 +286,13 @@ func (clients *clientsContainer) addFromConfig(
 
 		_, err = clients.add(cli)
 		if err != nil {
-			log.Error("clients: adding client at index %d %s: %s", i, cli.Name, err)
+			if errors.Is(err, client.ErrDuplicateUID) {
+				return fmt.Errorf("clients: adding client %s at index %d: %w", cli.Name, i, err)
+			}
+
+			// TODO(s.chzhen):  Return an error instead of logging if more
+			// stringent requirements are implemented.
+			log.Error("clients: adding client %s at index %d: %s", cli.Name, i, err)
 		}
 	}