diff --git a/elasticsearch/x-pack/marvel/src/main/java/org/elasticsearch/marvel/agent/resolver/shards/ShardsResolver.java b/elasticsearch/x-pack/marvel/src/main/java/org/elasticsearch/marvel/agent/resolver/shards/ShardsResolver.java
index ca4288b9617..c5064d7eb71 100644
--- a/elasticsearch/x-pack/marvel/src/main/java/org/elasticsearch/marvel/agent/resolver/shards/ShardsResolver.java
+++ b/elasticsearch/x-pack/marvel/src/main/java/org/elasticsearch/marvel/agent/resolver/shards/ShardsResolver.java
@@ -60,7 +60,7 @@ public class ShardsResolver extends MonitoringIndexNameResolver.Timestamped<Shar
         if (shardRouting != null) {
             // ShardRouting is rendered inside a startObject() / endObject() but without a name,
             // so we must use XContentBuilder.field(String, ToXContent, ToXContent.Params) here
-            builder.field(Fields.SHARD.underscore().toString(), shardRouting, params);
+            builder.field(Fields.SHARD.value(), shardRouting, params);
         }
     }
 
diff --git a/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/action/MonitoringBulkTests.java b/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/action/MonitoringBulkTests.java
index 68624cfd994..90d7ba2edab 100644
--- a/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/action/MonitoringBulkTests.java
+++ b/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/action/MonitoringBulkTests.java
@@ -58,9 +58,9 @@ public class MonitoringBulkTests extends MarvelIntegTestCase {
 
         for (SearchHit searchHit : searchResponse.getHits()) {
             Map<String, Object> source = searchHit.sourceAsMap();
-            assertNotNull(source.get(MonitoringBulkResolver.Fields.CLUSTER_UUID.underscore().toString()));
-            assertNotNull(source.get(MonitoringBulkResolver.Fields.TIMESTAMP.underscore().toString()));
-            assertNotNull(source.get(MonitoringBulkResolver.Fields.SOURCE_NODE.underscore().toString()));
+            assertNotNull(source.get(MonitoringBulkResolver.Fields.CLUSTER_UUID.value()));
+            assertNotNull(source.get(MonitoringBulkResolver.Fields.TIMESTAMP.value()));
+            assertNotNull(source.get(MonitoringBulkResolver.Fields.SOURCE_NODE.value()));
         }
     }
 
diff --git a/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/MonitoringIndexNameResolverTestCase.java b/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/MonitoringIndexNameResolverTestCase.java
index 3c2fdb0e9a1..bc4177cf787 100644
--- a/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/MonitoringIndexNameResolverTestCase.java
+++ b/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/MonitoringIndexNameResolverTestCase.java
@@ -148,9 +148,9 @@ public abstract class MonitoringIndexNameResolverTestCase<M extends MonitoringDo
         assertNotNull(sourceFields);
 
         String[] commons = new String[]{
-                CLUSTER_UUID.underscore().getValue(),
-                TIMESTAMP.underscore().getValue(),
-                SOURCE_NODE.underscore().getValue(),
+                CLUSTER_UUID.value(),
+                TIMESTAMP.value(),
+                SOURCE_NODE.value(),
         };
         assertThat("source must contains default fields", sourceFields.keySet(), hasItems(commons));
 
diff --git a/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/cluster/ClusterInfoTests.java b/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/cluster/ClusterInfoTests.java
index cd43fa476d9..16d3627f05e 100644
--- a/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/cluster/ClusterInfoTests.java
+++ b/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/cluster/ClusterInfoTests.java
@@ -77,42 +77,42 @@ public class ClusterInfoTests extends MarvelIntegTestCase {
         assertThat(response.getId(), equalTo(clusterUUID));
 
         Map<String, Object> source = response.getSource();
-        assertThat(source.get(MonitoringIndexNameResolver.Fields.CLUSTER_UUID.underscore().toString()), notNullValue());
-        assertThat(source.get(MonitoringIndexNameResolver.Fields.TIMESTAMP.underscore().toString()), notNullValue());
-        assertThat(source.get(MonitoringIndexNameResolver.Fields.SOURCE_NODE.underscore().toString()), notNullValue());
-        assertThat(source.get(ClusterInfoResolver.Fields.CLUSTER_NAME.underscore().toString()), equalTo(cluster().getClusterName()));
-        assertThat(source.get(ClusterInfoResolver.Fields.VERSION.underscore().toString()), equalTo(Version.CURRENT.toString()));
+        assertThat(source.get(MonitoringIndexNameResolver.Fields.CLUSTER_UUID.value()), notNullValue());
+        assertThat(source.get(MonitoringIndexNameResolver.Fields.TIMESTAMP.value()), notNullValue());
+        assertThat(source.get(MonitoringIndexNameResolver.Fields.SOURCE_NODE.value()), notNullValue());
+        assertThat(source.get(ClusterInfoResolver.Fields.CLUSTER_NAME.value()), equalTo(cluster().getClusterName()));
+        assertThat(source.get(ClusterInfoResolver.Fields.VERSION.value()), equalTo(Version.CURRENT.toString()));
 
         logger.debug("--> checking that the document contains license information");
-        Object licenseObj = source.get(ClusterInfoResolver.Fields.LICENSE.underscore().toString());
+        Object licenseObj = source.get(ClusterInfoResolver.Fields.LICENSE.value());
         assertThat(licenseObj, instanceOf(Map.class));
         Map license = (Map) licenseObj;
 
         assertThat(license, instanceOf(Map.class));
 
-        String uid = (String) license.get(ClusterInfoResolver.Fields.UID.underscore().toString());
+        String uid = (String) license.get(ClusterInfoResolver.Fields.UID.value());
         assertThat(uid, not(isEmptyOrNullString()));
 
-        String type = (String) license.get(ClusterInfoResolver.Fields.TYPE.underscore().toString());
+        String type = (String) license.get(ClusterInfoResolver.Fields.TYPE.value());
         assertThat(type, not(isEmptyOrNullString()));
 
-        String status = (String) license.get(License.XFields.STATUS.underscore().toString());
+        String status = (String) license.get(License.XFields.STATUS.value());
         assertThat(status, not(isEmptyOrNullString()));
 
-        Long expiryDate = (Long) license.get(License.XFields.EXPIRY_DATE_IN_MILLIS.underscore().toString());
+        Long expiryDate = (Long) license.get(License.XFields.EXPIRY_DATE_IN_MILLIS.value());
         assertThat(expiryDate, greaterThan(0L));
 
         // We basically recompute the hash here
-        String hkey = (String) license.get(ClusterInfoResolver.Fields.HKEY.underscore().toString());
+        String hkey = (String) license.get(ClusterInfoResolver.Fields.HKEY.value());
         String recalculated = ClusterInfoResolver.hash(status, uid, type, String.valueOf(expiryDate), clusterUUID);
         assertThat(hkey, equalTo(recalculated));
 
-        assertThat((String) license.get(License.XFields.ISSUER.underscore().toString()), not(isEmptyOrNullString()));
-        assertThat((String) license.get(License.XFields.ISSUED_TO.underscore().toString()), not(isEmptyOrNullString()));
-        assertThat((Long) license.get(License.XFields.ISSUE_DATE_IN_MILLIS.underscore().toString()), greaterThan(0L));
-        assertThat((Integer) license.get(License.XFields.MAX_NODES.underscore().toString()), greaterThan(0));
+        assertThat((String) license.get(License.XFields.ISSUER.value()), not(isEmptyOrNullString()));
+        assertThat((String) license.get(License.XFields.ISSUED_TO.value()), not(isEmptyOrNullString()));
+        assertThat((Long) license.get(License.XFields.ISSUE_DATE_IN_MILLIS.value()), greaterThan(0L));
+        assertThat((Integer) license.get(License.XFields.MAX_NODES.value()), greaterThan(0));
 
-        Object clusterStats = source.get(ClusterInfoResolver.Fields.CLUSTER_STATS.underscore().toString());
+        Object clusterStats = source.get(ClusterInfoResolver.Fields.CLUSTER_STATS.value());
         assertNotNull(clusterStats);
         assertThat(clusterStats, instanceOf(Map.class));
         assertThat(((Map) clusterStats).size(), greaterThan(0));
@@ -128,10 +128,10 @@ public class ClusterInfoTests extends MarvelIntegTestCase {
                 .setTypes(ClusterInfoResolver.TYPE)
                 .setQuery(
                     QueryBuilders.boolQuery()
-                        .should(QueryBuilders.matchQuery(License.XFields.STATUS.underscore().toString(), License.Status.ACTIVE.label()))
-                        .should(QueryBuilders.matchQuery(License.XFields.STATUS.underscore().toString(), License.Status.INVALID.label()))
-                        .should(QueryBuilders.matchQuery(License.XFields.STATUS.underscore().toString(), License.Status.EXPIRED.label()))
-                        .should(QueryBuilders.matchQuery(ClusterInfoResolver.Fields.CLUSTER_NAME.underscore().toString(),
+                        .should(QueryBuilders.matchQuery(License.XFields.STATUS.value(), License.Status.ACTIVE.label()))
+                        .should(QueryBuilders.matchQuery(License.XFields.STATUS.value(), License.Status.INVALID.label()))
+                        .should(QueryBuilders.matchQuery(License.XFields.STATUS.value(), License.Status.EXPIRED.label()))
+                        .should(QueryBuilders.matchQuery(ClusterInfoResolver.Fields.CLUSTER_NAME.value(),
                                 cluster().getClusterName()))
                         .minimumNumberShouldMatch(1)
                 ).get(), 0L);
diff --git a/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/cluster/ClusterStateTests.java b/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/cluster/ClusterStateTests.java
index f71e20ddc73..e58e13fd81c 100644
--- a/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/cluster/ClusterStateTests.java
+++ b/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/cluster/ClusterStateTests.java
@@ -122,13 +122,13 @@ public class ClusterStateTests extends MarvelIntegTestCase {
 
         logger.debug("--> checking that every document contains the expected fields");
         String[] filters = {
-                MonitoringIndexNameResolver.Fields.CLUSTER_UUID.underscore().toString(),
-                MonitoringIndexNameResolver.Fields.TIMESTAMP.underscore().toString(),
-                SOURCE_NODE.underscore().toString(),
-                ClusterStateNodeResolver.Fields.STATE_UUID.underscore().toString(),
-                ClusterStateNodeResolver.Fields.NODE.underscore().toString(),
-                ClusterStateNodeResolver.Fields.NODE.underscore().toString() + "."
-                        + ClusterStateNodeResolver.Fields.ID.underscore().toString(),
+                MonitoringIndexNameResolver.Fields.CLUSTER_UUID.value(),
+                MonitoringIndexNameResolver.Fields.TIMESTAMP.value(),
+                SOURCE_NODE.value(),
+                ClusterStateNodeResolver.Fields.STATE_UUID.value(),
+                ClusterStateNodeResolver.Fields.NODE.value(),
+                ClusterStateNodeResolver.Fields.NODE.value() + "."
+                        + ClusterStateNodeResolver.Fields.ID.value(),
         };
 
         for (SearchHit searchHit : response.getHits().getHits()) {
@@ -143,7 +143,7 @@ public class ClusterStateTests extends MarvelIntegTestCase {
         assertThat(client().prepareSearch().setSize(0)
                 .setIndices(timestampedIndex)
                 .setTypes(ClusterStateNodeResolver.TYPE)
-                .setQuery(QueryBuilders.matchQuery(SOURCE_NODE.underscore().toString() + ".attributes.custom", randomInt))
+                .setQuery(QueryBuilders.matchQuery(SOURCE_NODE.value() + ".attributes.custom", randomInt))
                 .get().getHits().getTotalHits(), greaterThan(0L));
 
         logger.debug("--> cluster state nodes successfully collected");
@@ -167,18 +167,18 @@ public class ClusterStateTests extends MarvelIntegTestCase {
 
         logger.debug("--> checking that every document contains the expected fields");
         String[] filters = {
-                MonitoringIndexNameResolver.Fields.CLUSTER_UUID.underscore().toString(),
-                MonitoringIndexNameResolver.Fields.TIMESTAMP.underscore().toString(),
-                MonitoringIndexNameResolver.Fields.SOURCE_NODE.underscore().toString(),
-                DiscoveryNodeResolver.Fields.NODE.underscore().toString(),
-                DiscoveryNodeResolver.Fields.NODE.underscore().toString() + "."
-                        + DiscoveryNodeResolver.Fields.ID.underscore().toString(),
-                DiscoveryNodeResolver.Fields.NODE.underscore().toString() + "."
-                        + DiscoveryNodeResolver.Fields.NAME.underscore().toString(),
-                DiscoveryNodeResolver.Fields.NODE.underscore().toString() + "."
-                        + DiscoveryNodeResolver.Fields.ATTRIBUTES.underscore().toString(),
-                DiscoveryNodeResolver.Fields.NODE.underscore().toString() + "."
-                        + DiscoveryNodeResolver.Fields.TRANSPORT_ADDRESS.underscore().toString(),
+                MonitoringIndexNameResolver.Fields.CLUSTER_UUID.value(),
+                MonitoringIndexNameResolver.Fields.TIMESTAMP.value(),
+                MonitoringIndexNameResolver.Fields.SOURCE_NODE.value(),
+                DiscoveryNodeResolver.Fields.NODE.value(),
+                DiscoveryNodeResolver.Fields.NODE.value() + "."
+                        + DiscoveryNodeResolver.Fields.ID.value(),
+                DiscoveryNodeResolver.Fields.NODE.value() + "."
+                        + DiscoveryNodeResolver.Fields.NAME.value(),
+                DiscoveryNodeResolver.Fields.NODE.value() + "."
+                        + DiscoveryNodeResolver.Fields.ATTRIBUTES.value(),
+                DiscoveryNodeResolver.Fields.NODE.value() + "."
+                        + DiscoveryNodeResolver.Fields.TRANSPORT_ADDRESS.value(),
         };
 
         for (SearchHit searchHit : response.getHits().getHits()) {
diff --git a/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/indices/IndexRecoveryTests.java b/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/indices/IndexRecoveryTests.java
index 41f155d85da..1f15944cf66 100644
--- a/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/indices/IndexRecoveryTests.java
+++ b/elasticsearch/x-pack/marvel/src/test/java/org/elasticsearch/marvel/agent/resolver/indices/IndexRecoveryTests.java
@@ -80,12 +80,12 @@ public class IndexRecoveryTests extends MarvelIntegTestCase {
 
         logger.debug("--> checking that every document contains the expected fields");
         String[] filters = {
-                MonitoringIndexNameResolver.Fields.CLUSTER_UUID.underscore().toString(),
-                MonitoringIndexNameResolver.Fields.TIMESTAMP.underscore().toString(),
-                MonitoringIndexNameResolver.Fields.SOURCE_NODE.underscore().toString(),
-                IndexRecoveryResolver.Fields.INDEX_RECOVERY.underscore().toString(),
-                IndexRecoveryResolver.Fields.INDEX_RECOVERY.underscore().toString() + "."
-                        + IndexRecoveryResolver.Fields.SHARDS.underscore().toString(),
+                MonitoringIndexNameResolver.Fields.CLUSTER_UUID.value(),
+                MonitoringIndexNameResolver.Fields.TIMESTAMP.value(),
+                MonitoringIndexNameResolver.Fields.SOURCE_NODE.value(),
+                IndexRecoveryResolver.Fields.INDEX_RECOVERY.value(),
+                IndexRecoveryResolver.Fields.INDEX_RECOVERY.value() + "."
+                        + IndexRecoveryResolver.Fields.SHARDS.value(),
         };
 
         for (SearchHit searchHit : response.getHits().getHits()) {