diff --git a/server/src/main/java/org/elasticsearch/action/admin/cluster/reroute/ClusterRerouteResponse.java b/server/src/main/java/org/elasticsearch/action/admin/cluster/reroute/ClusterRerouteResponse.java
index f3233f4147ea8..caf9fa62d4cd1 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/cluster/reroute/ClusterRerouteResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/cluster/reroute/ClusterRerouteResponse.java
@@ -19,7 +19,9 @@
 
 package org.elasticsearch.action.admin.cluster.reroute;
 
+import org.elasticsearch.Version;
 import org.elasticsearch.action.support.master.AcknowledgedResponse;
+import org.elasticsearch.cluster.ClusterModule;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.routing.allocation.RoutingExplanations;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -70,7 +72,11 @@ public void readFrom(StreamInput in) throws IOException {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
-        state.writeTo(out);
+        if (out.getVersion().onOrAfter(Version.V_6_3_0)) {
+            state.writeTo(out);
+        } else {
+            ClusterModule.filterCustomsForPre63Clients(state).writeTo(out);
+        }
         writeAcknowledged(out);
         RoutingExplanations.writeTo(explanations, out);
     }
diff --git a/server/src/main/java/org/elasticsearch/action/admin/cluster/state/ClusterStateResponse.java b/server/src/main/java/org/elasticsearch/action/admin/cluster/state/ClusterStateResponse.java
index cdc869e529d3b..71ad6f9f83476 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/cluster/state/ClusterStateResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/cluster/state/ClusterStateResponse.java
@@ -21,6 +21,7 @@
 
 import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionResponse;
+import org.elasticsearch.cluster.ClusterModule;
 import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -94,7 +95,11 @@ public void readFrom(StreamInput in) throws IOException {
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         clusterName.writeTo(out);
-        clusterState.writeTo(out);
+        if (out.getVersion().onOrAfter(Version.V_6_3_0)) {
+            clusterState.writeTo(out);
+        } else {
+            ClusterModule.filterCustomsForPre63Clients(clusterState).writeTo(out);
+        }
         if (out.getVersion().onOrAfter(Version.V_6_0_0_alpha1)) {
             totalCompressedSize.writeTo(out);
         }
diff --git a/server/src/main/java/org/elasticsearch/cluster/ClusterModule.java b/server/src/main/java/org/elasticsearch/cluster/ClusterModule.java
index 7f16c3f85ffc6..9c5c642df6b91 100644
--- a/server/src/main/java/org/elasticsearch/cluster/ClusterModule.java
+++ b/server/src/main/java/org/elasticsearch/cluster/ClusterModule.java
@@ -66,6 +66,7 @@
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Setting.Property;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.util.set.Sets;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
 import org.elasticsearch.gateway.GatewayAllocator;
 import org.elasticsearch.ingest.IngestMetadata;
@@ -84,6 +85,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
 import java.util.function.Function;
 import java.util.function.Supplier;
 
@@ -150,6 +152,35 @@ public static List<Entry> getNamedWriteables() {
         return entries;
     }
 
+    static final Set<String> PRE_6_3_METADATA_CUSTOMS_WHITE_LIST = Collections.unmodifiableSet(Sets.newHashSet(
+        IndexGraveyard.TYPE, IngestMetadata.TYPE, RepositoriesMetaData.TYPE, ScriptMetaData.TYPE));
+
+    static final Set<String> PRE_6_3_CLUSTER_CUSTOMS_WHITE_LIST = Collections.unmodifiableSet(Sets.newHashSet(
+        RestoreInProgress.TYPE, SnapshotDeletionsInProgress.TYPE, SnapshotsInProgress.TYPE));
+
+    /**
+     * For interoperability with transport clients older than 6.3, we need to strip customs
+     * from the cluster state that the client might not be able to deserialize
+     *
+     * @param clusterState the cluster state to filter the customs from
+     * @return the adapted cluster state
+     */
+    public static ClusterState filterCustomsForPre63Clients(ClusterState clusterState) {
+        final ClusterState.Builder builder = ClusterState.builder(clusterState);
+        clusterState.customs().keysIt().forEachRemaining(name -> {
+            if (PRE_6_3_CLUSTER_CUSTOMS_WHITE_LIST.contains(name) == false) {
+                builder.removeCustom(name);
+            }
+        });
+        final MetaData.Builder metaBuilder = MetaData.builder(clusterState.metaData());
+        clusterState.metaData().customs().keysIt().forEachRemaining(name -> {
+            if (PRE_6_3_METADATA_CUSTOMS_WHITE_LIST.contains(name) == false) {
+                metaBuilder.removeCustom(name);
+            }
+        });
+        return builder.metaData(metaBuilder).build();
+    }
+
     public static List<NamedXContentRegistry.Entry> getNamedXWriteables() {
         List<NamedXContentRegistry.Entry> entries = new ArrayList<>();
         // Metadata
diff --git a/server/src/test/java/org/elasticsearch/cluster/ClusterModuleTests.java b/server/src/test/java/org/elasticsearch/cluster/ClusterModuleTests.java
index 176616690f0aa..efd8026645249 100644
--- a/server/src/test/java/org/elasticsearch/cluster/ClusterModuleTests.java
+++ b/server/src/test/java/org/elasticsearch/cluster/ClusterModuleTests.java
@@ -19,6 +19,8 @@
 
 package org.elasticsearch.cluster;
 
+import org.elasticsearch.cluster.metadata.MetaData;
+import org.elasticsearch.cluster.metadata.RepositoriesMetaData;
 import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.cluster.routing.allocation.RoutingAllocation;
 import org.elasticsearch.cluster.routing.allocation.ShardAllocationDecision;
@@ -251,4 +253,29 @@ public Map<String, Supplier<ClusterState.Custom>> getInitialClusterStateCustomSu
             assertEquals(ise.getMessage(), "custom supplier key [foo] is registered more than once");
         }
     }
+
+    public void testPre63CustomsFiltering() {
+        final String whiteListedClusterCustom = randomFrom(ClusterModule.PRE_6_3_CLUSTER_CUSTOMS_WHITE_LIST);
+        final String whiteListedMetaDataCustom = randomFrom(ClusterModule.PRE_6_3_METADATA_CUSTOMS_WHITE_LIST);
+        final ClusterState clusterState = ClusterState.builder(ClusterName.DEFAULT)
+            .putCustom(whiteListedClusterCustom, new RestoreInProgress())
+            .putCustom("other", new RestoreInProgress())
+            .metaData(MetaData.builder()
+                .putCustom(whiteListedMetaDataCustom, new RepositoriesMetaData(Collections.emptyList()))
+                .putCustom("other", new RepositoriesMetaData(Collections.emptyList()))
+                .build())
+            .build();
+
+        assertNotNull(clusterState.custom(whiteListedClusterCustom));
+        assertNotNull(clusterState.custom("other"));
+        assertNotNull(clusterState.metaData().custom(whiteListedMetaDataCustom));
+        assertNotNull(clusterState.metaData().custom("other"));
+
+        final ClusterState fixedClusterState = ClusterModule.filterCustomsForPre63Clients(clusterState);
+
+        assertNotNull(fixedClusterState.custom(whiteListedClusterCustom));
+        assertNull(fixedClusterState.custom("other"));
+        assertNotNull(fixedClusterState.metaData().custom(whiteListedMetaDataCustom));
+        assertNull(fixedClusterState.metaData().custom("other"));
+    }
 }