diff --git a/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/FollowExistingIndexAction.java b/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/FollowExistingIndexAction.java
index 0ea6de6fe7b..c200acf9ad7 100644
--- a/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/FollowExistingIndexAction.java
+++ b/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/FollowExistingIndexAction.java
@@ -156,12 +156,14 @@ public class FollowExistingIndexAction extends Action<FollowExistingIndexAction.
                             .index(request.leaderIndex);
                     if (leaderIndexMetadata == null) {
                         listener.onFailure(new IllegalArgumentException("leader index [" + request.leaderIndex + "] does not exist"));
+                        return;
                     }
 
                     IndexMetaData followIndexMetadata = clusterStateResponse.getState().getMetaData()
                             .index(request.followIndex);
                     if (followIndexMetadata == null) {
                         listener.onFailure(new IllegalArgumentException("follow index [" + request.followIndex + "] does not exist"));
+                        return;
                     }
 
                     if (leaderIndexMetadata.getNumberOfShards() != followIndexMetadata.getNumberOfShards()) {
diff --git a/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/ShardChangesIT.java b/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/ShardChangesIT.java
index 4c12ab5e6f6..0ea0b5c8295 100644
--- a/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/ShardChangesIT.java
+++ b/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/ShardChangesIT.java
@@ -34,15 +34,15 @@ import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.index.translog.Translog;
+import org.elasticsearch.persistent.PersistentTasksCustomMetaData;
 import org.elasticsearch.plugins.Plugin;
 import org.elasticsearch.test.ESIntegTestCase;
 import org.elasticsearch.test.discovery.TestZenDiscovery;
-import org.elasticsearch.xpack.core.XPackSettings;
 import org.elasticsearch.xpack.ccr.action.FollowExistingIndexAction;
 import org.elasticsearch.xpack.ccr.action.ShardChangesAction;
 import org.elasticsearch.xpack.ccr.action.ShardFollowTask;
 import org.elasticsearch.xpack.ccr.action.UnfollowIndexAction;
-import org.elasticsearch.persistent.PersistentTasksCustomMetaData;
+import org.elasticsearch.xpack.core.XPackSettings;
 
 import java.io.IOException;
 import java.util.Arrays;
@@ -219,6 +219,24 @@ public class ShardChangesIT extends ESIntegTestCase {
         });
     }
 
+    public void testFollowNonExistentIndex() throws Exception {
+        assertAcked(client().admin().indices().prepareCreate("test-leader").get());
+        assertAcked(client().admin().indices().prepareCreate("test-follower").get());
+        final FollowExistingIndexAction.Request followRequest = new FollowExistingIndexAction.Request();
+        // Leader index does not exist.
+        followRequest.setLeaderIndex("non-existent-leader");
+        followRequest.setFollowIndex("test-follower");
+        expectThrows(IllegalArgumentException.class, () -> client().execute(FollowExistingIndexAction.INSTANCE, followRequest).actionGet());
+        // Follower index does not exist.
+        followRequest.setLeaderIndex("test-leader");
+        followRequest.setFollowIndex("non-existent-follower");
+        expectThrows(IllegalArgumentException.class, () -> client().execute(FollowExistingIndexAction.INSTANCE, followRequest).actionGet());
+        // Both indices do not exist.
+        followRequest.setLeaderIndex("non-existent-leader");
+        followRequest.setFollowIndex("non-existent-follower");
+        expectThrows(IllegalArgumentException.class, () -> client().execute(FollowExistingIndexAction.INSTANCE, followRequest).actionGet());
+    }
+
     private CheckedRunnable<Exception> assertTask(final int numberOfPrimaryShards, final Map<ShardId, Long> numDocsPerShard) {
         return () -> {
             final ClusterState clusterState = client().admin().cluster().prepareState().get().getState();