diff --git a/backend/internal/service/ldap_service.go b/backend/internal/service/ldap_service.go
index c2da1d2e..2481c881 100644
--- a/backend/internal/service/ldap_service.go
+++ b/backend/internal/service/ldap_service.go
@@ -13,6 +13,9 @@ import (
 	"net/url"
 	"strings"
 	"time"
+	"unicode/utf8"
+
+	"github.com/google/uuid"
 
 	"github.com/go-ldap/ldap/v3"
 	"github.com/pocket-id/pocket-id/backend/internal/common"
@@ -122,7 +125,7 @@ func (s *LdapService) SyncGroups(ctx context.Context, tx *gorm.DB, client *ldap.
 	ldapGroupIDs := make(map[string]struct{}, len(result.Entries))
 
 	for _, value := range result.Entries {
-		ldapId := value.GetAttributeValue(dbConfig.LdapAttributeGroupUniqueIdentifier.Value)
+		ldapId := convertLdapIdToString(value.GetAttributeValue(dbConfig.LdapAttributeGroupUniqueIdentifier.Value))
 
 		// Skip groups without a valid LDAP ID
 		if ldapId == "" {
@@ -194,7 +197,7 @@ func (s *LdapService) SyncGroups(ctx context.Context, tx *gorm.DB, client *ldap.
 		syncGroup := dto.UserGroupCreateDto{
 			Name:         value.GetAttributeValue(dbConfig.LdapAttributeGroupName.Value),
 			FriendlyName: value.GetAttributeValue(dbConfig.LdapAttributeGroupName.Value),
-			LdapID:       value.GetAttributeValue(dbConfig.LdapAttributeGroupUniqueIdentifier.Value),
+			LdapID:       ldapId,
 		}
 
 		if databaseGroup.ID == "" {
@@ -286,7 +289,7 @@ func (s *LdapService) SyncUsers(ctx context.Context, tx *gorm.DB, client *ldap.C
 	ldapUserIDs := make(map[string]struct{}, len(result.Entries))
 
 	for _, value := range result.Entries {
-		ldapId := value.GetAttributeValue(dbConfig.LdapAttributeUserUniqueIdentifier.Value)
+		ldapId := convertLdapIdToString(value.GetAttributeValue(dbConfig.LdapAttributeUserUniqueIdentifier.Value))
 
 		// Skip users without a valid LDAP ID
 		if ldapId == "" {
@@ -468,3 +471,21 @@ func getDNProperty(property string, str string) string {
 	// CN not found, return an empty string
 	return ""
 }
+
+// convertLdapIdToString converts LDAP IDs to valid UTF-8 strings.
+// LDAP servers may return binary UUIDs (16 bytes) or other non-UTF-8 data.
+func convertLdapIdToString(ldapId string) string {
+	if utf8.ValidString(ldapId) {
+		return ldapId
+	}
+
+	// Try to parse as binary UUID (16 bytes)
+	if len(ldapId) == 16 {
+		if parsedUUID, err := uuid.FromBytes([]byte(ldapId)); err == nil {
+			return parsedUUID.String()
+		}
+	}
+
+	// As a last resort, encode as base64 to make it UTF-8 safe
+	return base64.StdEncoding.EncodeToString([]byte(ldapId))
+}
diff --git a/backend/internal/service/ldap_service_test.go b/backend/internal/service/ldap_service_test.go
index 3a3e8c0b..1a049bfe 100644
--- a/backend/internal/service/ldap_service_test.go
+++ b/backend/internal/service/ldap_service_test.go
@@ -71,3 +71,36 @@ func TestGetDNProperty(t *testing.T) {
 		})
 	}
 }
+
+func TestConvertLdapIdToString(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "valid UTF-8 string",
+			input:    "simple-utf8-id",
+			expected: "simple-utf8-id",
+		},
+		{
+			name:     "binary UUID (16 bytes)",
+			input:    string([]byte{0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0, 0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf1}),
+			expected: "12345678-9abc-def0-1234-56789abcdef1",
+		},
+		{
+			name:     "non-UTF8, non-UUID returns base64",
+			input:    string([]byte{0xff, 0xfe, 0xfd, 0xfc}),
+			expected: "//79/A==",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := convertLdapIdToString(tt.input)
+			if got != tt.expected {
+				t.Errorf("Expected %q, got %q", tt.expected, got)
+			}
+		})
+	}
+}