diff --git a/model/map/src/main/java/org/keycloak/models/map/client/MapClientAdapter.java b/model/map/src/main/java/org/keycloak/models/map/client/MapClientAdapter.java
index d1ac011ac6..55b3961a11 100644
--- a/model/map/src/main/java/org/keycloak/models/map/client/MapClientAdapter.java
+++ b/model/map/src/main/java/org/keycloak/models/map/client/MapClientAdapter.java
@@ -16,6 +16,7 @@
  */
 package org.keycloak.models.map.client;
 
+import org.jboss.logging.Logger;
 import org.keycloak.models.ClientModel;
 import org.keycloak.models.KeycloakSession;
 import org.keycloak.models.ProtocolMapperModel;
@@ -39,6 +40,7 @@ import java.util.stream.Stream;
  */
 public abstract class MapClientAdapter extends AbstractClientModel<MapClientEntity> implements ClientModel {
 
+    private static final Logger LOG = Logger.getLogger(MapClientAdapter.class);
     private final MapProtocolMapperUtils pmUtils;
 
     public MapClientAdapter(KeycloakSession session, RealmModel realm, MapClientEntity entity) {
@@ -286,7 +288,15 @@ public abstract class MapClientAdapter extends AbstractClientModel<MapClientEnti
         final Map<String, List<String>> a = attributes == null ? Collections.emptyMap() : attributes;
         return a.entrySet().stream().collect(Collectors.toMap(Map.Entry::getKey,
             entry -> {
-                if (entry.getValue().isEmpty()) return null;
+                if (entry.getValue().isEmpty()) {
+                    return null;
+                } else if (entry.getValue().size() > 1) {
+                    // This could be caused by an inconsistency in the storage, a programming error,
+                    // or a downgrade from a future version of Keycloak that already supports multi-valued attributes.
+                    // The caller will not see the other values, and when this entity is later updated, the additional values will be lost.
+                    LOG.warnf("Client '%s' realm '%s' has attribute '%s' with %d values, retrieving only the first", getClientId(), getRealm().getName(), entry.getKey(),
+                            entry.getValue().size());
+                }
                 return entry.getValue().get(0);
             })
         );
diff --git a/model/map/src/main/java/org/keycloak/models/map/clientscope/MapClientScopeAdapter.java b/model/map/src/main/java/org/keycloak/models/map/clientscope/MapClientScopeAdapter.java
index 1ea41cbb2d..afe84db777 100644
--- a/model/map/src/main/java/org/keycloak/models/map/clientscope/MapClientScopeAdapter.java
+++ b/model/map/src/main/java/org/keycloak/models/map/clientscope/MapClientScopeAdapter.java
@@ -25,6 +25,8 @@ import java.util.Objects;
 import java.util.Set;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
+
+import org.jboss.logging.Logger;
 import org.keycloak.models.ClientScopeModel;
 import org.keycloak.models.KeycloakSession;
 import org.keycloak.models.ProtocolMapperModel;
@@ -37,6 +39,7 @@ import org.keycloak.models.utils.RoleUtils;
 
 public class MapClientScopeAdapter extends AbstractClientScopeModel<MapClientScopeEntity> implements ClientScopeModel {
 
+    private static final Logger LOG = Logger.getLogger(MapClientScopeAdapter.class);
     private final MapProtocolMapperUtils pmUtils;
 
     public MapClientScopeAdapter(KeycloakSession session, RealmModel realm, MapClientScopeEntity entity) {
@@ -115,7 +118,15 @@ public class MapClientScopeAdapter extends AbstractClientScopeModel<MapClientSco
         final Map<String, List<String>> a = attributes == null ? Collections.emptyMap() : attributes;
         return a.entrySet().stream().collect(Collectors.toMap(Map.Entry::getKey,
             entry -> {
-                if (entry.getValue().isEmpty()) return null;
+                if (entry.getValue().isEmpty()) {
+                    return null;
+                } else if (entry.getValue().size() > 1) {
+                    // This could be caused by an inconsistency in the storage, a programming error,
+                    // or a downgrade from a future version of Keycloak that already supports multi-valued attributes.
+                    // The caller will not see the other values, and when this entity is later updated, the additional values will be lost.
+                    LOG.warnf("ClientScope '%s' realm '%s' has attribute '%s' with %d values, retrieving only the first", getName(), getRealm().getName(), entry.getKey(),
+                            entry.getValue().size());
+                }
                 return entry.getValue().get(0);
             })
         );
diff --git a/model/map/src/main/java/org/keycloak/models/map/realm/MapRealmAdapter.java b/model/map/src/main/java/org/keycloak/models/map/realm/MapRealmAdapter.java
index 2b0fd3e24b..a4f8c18c15 100644
--- a/model/map/src/main/java/org/keycloak/models/map/realm/MapRealmAdapter.java
+++ b/model/map/src/main/java/org/keycloak/models/map/realm/MapRealmAdapter.java
@@ -24,6 +24,8 @@ import static java.util.Objects.nonNull;
 import java.util.Set;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
+
+import org.jboss.logging.Logger;
 import org.keycloak.Config;
 import org.keycloak.common.enums.SslRequired;
 import org.keycloak.component.ComponentFactory;
@@ -64,6 +66,7 @@ import org.keycloak.models.utils.ComponentUtil;
 
 public class MapRealmAdapter extends AbstractRealmModel<MapRealmEntity> implements RealmModel {
 
+    private static final Logger LOG = Logger.getLogger(MapRealmAdapter.class);
     private static final String ACTION_TOKEN_GENERATED_BY_USER_LIFESPAN = "actionTokenGeneratedByUserLifespan";
     private static final String DEFAULT_SIGNATURE_ALGORITHM = "defaultSignatureAlgorithm";
     private static final String BRUTE_FORCE_PROTECTED = "bruteForceProtected";
@@ -207,7 +210,15 @@ public class MapRealmAdapter extends AbstractRealmModel<MapRealmEntity> implemen
     public Map<String, String> getAttributes() {
         return entity.getAttributes().entrySet().stream().collect(Collectors.toMap(Map.Entry::getKey, 
             entry -> {
-                if (entry.getValue().isEmpty()) return null;
+                if (entry.getValue().isEmpty()) {
+                    return null;
+                } else if (entry.getValue().size() > 1) {
+                    // This could be caused by an inconsistency in the storage, a programming error,
+                    // or a downgrade from a future version of Keycloak that already supports multi-valued attributes.
+                    // The caller will not see the other values, and when this entity is later updated, the additional values be will lost.
+                    LOG.warnf("Realm '%s' has attribute '%s' with %d values, retrieving only the first", getId(), entry.getKey(),
+                            entry.getValue().size());
+                }
                 return entry.getValue().get(0);
             })
         );