diff --git a/core/src/main/java/org/elasticsearch/gateway/BaseGatewayShardAllocator.java b/core/src/main/java/org/elasticsearch/gateway/BaseGatewayShardAllocator.java
index 1b2d8b794f5..275311cf6a8 100644
--- a/core/src/main/java/org/elasticsearch/gateway/BaseGatewayShardAllocator.java
+++ b/core/src/main/java/org/elasticsearch/gateway/BaseGatewayShardAllocator.java
@@ -20,14 +20,20 @@
 package org.elasticsearch.gateway;
 
 import org.apache.logging.log4j.Logger;
+import org.elasticsearch.cluster.routing.RoutingNode;
 import org.elasticsearch.cluster.routing.RoutingNodes;
 import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.cluster.routing.allocation.AllocateUnassignedDecision;
 import org.elasticsearch.cluster.routing.allocation.AllocationDecision;
+import org.elasticsearch.cluster.routing.allocation.NodeAllocationResult;
 import org.elasticsearch.cluster.routing.allocation.RoutingAllocation;
+import org.elasticsearch.cluster.routing.allocation.decider.Decision;
 import org.elasticsearch.common.component.AbstractComponent;
 import org.elasticsearch.common.settings.Settings;
 
+import java.util.ArrayList;
+import java.util.List;
+
 /**
  * An abstract class that implements basic functionality for allocating
  * shards to nodes based on shard copies that already exist in the cluster.
@@ -85,4 +91,17 @@ public abstract class BaseGatewayShardAllocator extends AbstractComponent {
     public abstract AllocateUnassignedDecision makeAllocationDecision(ShardRouting unassignedShard,
                                                                       RoutingAllocation allocation,
                                                                       Logger logger);
+
+    /**
+     * Builds decisions for all nodes in the cluster, so that the explain API can provide information on
+     * allocation decisions for each node, while still waiting to allocate the shard (e.g. due to fetching shard data).
+     */
+    protected List<NodeAllocationResult> buildDecisionsForAllNodes(ShardRouting shard, RoutingAllocation allocation) {
+        List<NodeAllocationResult> results = new ArrayList<>();
+        for (RoutingNode node : allocation.routingNodes()) {
+            Decision decision = allocation.deciders().canAllocate(shard, node, allocation);
+            results.add(new NodeAllocationResult(node.node(), null, decision));
+        }
+        return results;
+    }
 }
diff --git a/core/src/main/java/org/elasticsearch/gateway/PrimaryShardAllocator.java b/core/src/main/java/org/elasticsearch/gateway/PrimaryShardAllocator.java
index 2a858dd6e85..2200ed1b4f2 100644
--- a/core/src/main/java/org/elasticsearch/gateway/PrimaryShardAllocator.java
+++ b/core/src/main/java/org/elasticsearch/gateway/PrimaryShardAllocator.java
@@ -124,9 +124,11 @@ public abstract class PrimaryShardAllocator extends BaseGatewayShardAllocator {
         final FetchResult<NodeGatewayStartedShards> shardState = fetchData(unassignedShard, allocation);
         if (shardState.hasData() == false) {
             allocation.setHasPendingAsyncFetch();
-            if (explain == false) {
-                return AllocateUnassignedDecision.no(AllocationStatus.FETCHING_SHARD_DATA, null);
+            List<NodeAllocationResult> nodeDecisions = null;
+            if (explain) {
+                nodeDecisions = buildDecisionsForAllNodes(unassignedShard, allocation);
             }
+            return AllocateUnassignedDecision.no(AllocationStatus.FETCHING_SHARD_DATA, nodeDecisions);
         }
 
         // don't create a new IndexSetting object for every shard as this could cause a lot of garbage
diff --git a/core/src/main/java/org/elasticsearch/gateway/ReplicaShardAllocator.java b/core/src/main/java/org/elasticsearch/gateway/ReplicaShardAllocator.java
index a5f3bd6a8fb..3a838ef3785 100644
--- a/core/src/main/java/org/elasticsearch/gateway/ReplicaShardAllocator.java
+++ b/core/src/main/java/org/elasticsearch/gateway/ReplicaShardAllocator.java
@@ -238,19 +238,6 @@ public abstract class ReplicaShardAllocator extends BaseGatewayShardAllocator {
         return AllocateUnassignedDecision.NOT_TAKEN;
     }
 
-    /**
-     * Builds decisions for all nodes in the cluster, so that the explain API can provide information on
-     * allocation decisions for each node, while still waiting to allocate the shard (e.g. due to fetching shard data).
-     */
-    private List<NodeAllocationResult> buildDecisionsForAllNodes(ShardRouting shard, RoutingAllocation allocation) {
-        List<NodeAllocationResult> results = new ArrayList<>();
-        for (RoutingNode node : allocation.routingNodes()) {
-            Decision decision = allocation.deciders().canAllocate(shard, node, allocation);
-            results.add(new NodeAllocationResult(node.node(), null, decision));
-        }
-        return results;
-    }
-
     /**
      * Determines if the shard can be allocated on at least one node based on the allocation deciders.
      *