diff --git a/core/src/main/java/org/elasticsearch/action/search/MultiSearchResponse.java b/core/src/main/java/org/elasticsearch/action/search/MultiSearchResponse.java
index 56e36e3d82f..0d7ae75d66f 100644
--- a/core/src/main/java/org/elasticsearch/action/search/MultiSearchResponse.java
+++ b/core/src/main/java/org/elasticsearch/action/search/MultiSearchResponse.java
@@ -20,6 +20,7 @@
 package org.elasticsearch.action.search;
 
 import com.google.common.collect.Iterators;
+import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -31,6 +32,7 @@ import org.elasticsearch.common.xcontent.XContentBuilderString;
 import org.elasticsearch.common.xcontent.XContentFactory;
 
 import java.io.IOException;
+import java.util.Collections;
 import java.util.Iterator;
 
 /**
@@ -43,22 +45,22 @@ public class MultiSearchResponse extends ActionResponse implements Iterable<Mult
      */
     public static class Item implements Streamable {
         private SearchResponse response;
-        private String failureMessage;
+        private Throwable throwable;
 
         Item() {
 
         }
 
-        public Item(SearchResponse response, String failureMessage) {
+        public Item(SearchResponse response, Throwable throwable) {
             this.response = response;
-            this.failureMessage = failureMessage;
+            this.throwable = throwable;
         }
 
         /**
          * Is it a failed search?
          */
         public boolean isFailure() {
-            return failureMessage != null;
+            return throwable != null;
         }
 
         /**
@@ -66,7 +68,7 @@ public class MultiSearchResponse extends ActionResponse implements Iterable<Mult
          */
         @Nullable
         public String getFailureMessage() {
-            return failureMessage;
+            return throwable == null ? null : throwable.getMessage();
         }
 
         /**
@@ -89,7 +91,7 @@ public class MultiSearchResponse extends ActionResponse implements Iterable<Mult
                 this.response = new SearchResponse();
                 response.readFrom(in);
             } else {
-                failureMessage = in.readString();
+                throwable = in.readThrowable();
             }
         }
 
@@ -100,9 +102,13 @@ public class MultiSearchResponse extends ActionResponse implements Iterable<Mult
                 response.writeTo(out);
             } else {
                 out.writeBoolean(false);
-                out.writeString(failureMessage);
+                out.writeThrowable(throwable);
             }
         }
+
+        public Throwable getFailure() {
+            return throwable;
+        }
     }
 
     private Item[] items;
@@ -150,7 +156,19 @@ public class MultiSearchResponse extends ActionResponse implements Iterable<Mult
         for (Item item : items) {
             if (item.isFailure()) {
                 builder.startObject();
-                builder.field(Fields.ERROR, item.getFailureMessage());
+                builder.startObject(Fields.ERROR);
+                final Throwable t = item.getFailure();
+                final ElasticsearchException[] rootCauses = ElasticsearchException.guessRootCauses(t);
+                builder.field(Fields.ROOT_CAUSE);
+                builder.startArray();
+                for (ElasticsearchException rootCause : rootCauses){
+                    builder.startObject();
+                    rootCause.toXContent(builder, new ToXContent.DelegatingMapParams(Collections.singletonMap(ElasticsearchException.REST_EXCEPTION_SKIP_CAUSE, "true"), params));
+                    builder.endObject();
+                }
+                builder.endArray();
+                ElasticsearchException.toXContent(builder, params, t);
+                builder.endObject();
                 builder.endObject();
             } else {
                 builder.startObject();
@@ -165,6 +183,7 @@ public class MultiSearchResponse extends ActionResponse implements Iterable<Mult
     static final class Fields {
         static final XContentBuilderString RESPONSES = new XContentBuilderString("responses");
         static final XContentBuilderString ERROR = new XContentBuilderString("error");
+        static final XContentBuilderString ROOT_CAUSE = new XContentBuilderString("root_cause");
     }
     
     @Override
diff --git a/core/src/main/java/org/elasticsearch/action/search/TransportMultiSearchAction.java b/core/src/main/java/org/elasticsearch/action/search/TransportMultiSearchAction.java
index a3d8f1c5359..e55caeffe5f 100644
--- a/core/src/main/java/org/elasticsearch/action/search/TransportMultiSearchAction.java
+++ b/core/src/main/java/org/elasticsearch/action/search/TransportMultiSearchAction.java
@@ -69,7 +69,7 @@ public class TransportMultiSearchAction extends HandledTransportAction<MultiSear
 
                 @Override
                 public void onFailure(Throwable e) {
-                    responses.set(index, new MultiSearchResponse.Item(null, ExceptionsHelper.detailedMessage(e)));
+                    responses.set(index, new MultiSearchResponse.Item(null, e));
                     if (counter.decrementAndGet() == 0) {
                         finishHim();
                     }
diff --git a/core/src/test/java/org/elasticsearch/action/search/MultiSearchRequestTests.java b/core/src/test/java/org/elasticsearch/action/search/MultiSearchRequestTests.java
index ee520760b53..9fbfd3914f2 100644
--- a/core/src/test/java/org/elasticsearch/action/search/MultiSearchRequestTests.java
+++ b/core/src/test/java/org/elasticsearch/action/search/MultiSearchRequestTests.java
@@ -21,9 +21,14 @@ package org.elasticsearch.action.search;
 
 import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.common.io.Streams;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.test.ElasticsearchTestCase;
 import org.junit.Test;
 
+import java.io.IOException;
+
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.nullValue;
 
@@ -114,4 +119,12 @@ public class MultiSearchRequestTests extends ElasticsearchTestCase {
         assertThat(request.requests().get(2).types()[1], equalTo("type1"));
         assertThat(request.requests().get(2).routing(), equalTo("123"));
     }
+
+    public void testResponseErrorToXContent() throws IOException {
+        MultiSearchResponse response = new MultiSearchResponse(new MultiSearchResponse.Item[]{new MultiSearchResponse.Item(null, new IllegalStateException("foobar")), new MultiSearchResponse.Item(null, new IllegalStateException("baaaaaazzzz"))});
+        XContentBuilder builder = XContentFactory.jsonBuilder();
+        response.toXContent(builder, ToXContent.EMPTY_PARAMS);
+        assertEquals("\"responses\"[{\"error\":{\"root_cause\":[{\"type\":\"illegal_state_exception\",\"reason\":\"foobar\"}],\"type\":\"illegal_state_exception\",\"reason\":\"foobar\"}},{\"error\":{\"root_cause\":[{\"type\":\"illegal_state_exception\",\"reason\":\"baaaaaazzzz\"}],\"type\":\"illegal_state_exception\",\"reason\":\"baaaaaazzzz\"}}]",
+                builder.string());
+    }
 }
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/test/msearch/10_basic.yaml b/rest-api-spec/src/main/resources/rest-api-spec/test/msearch/10_basic.yaml
index a028853429e..76ef7c42303 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/test/msearch/10_basic.yaml
+++ b/rest-api-spec/src/main/resources/rest-api-spec/test/msearch/10_basic.yaml
@@ -39,7 +39,9 @@
               match: {foo: bar}
 
   - match:  { responses.0.hits.total:     3  }
-  - match:  { responses.1.error: "/IndexMissingException.no.such.index./"  }
+  - match:  { responses.1.error.root_cause.0.type: index_missing_exception }
+  - match:  { responses.1.error.root_cause.0.reason: "/no.such.index/" }
+  - match:  { responses.1.error.root_cause.0.index: test_2 }
   - match:  { responses.2.hits.total:     1  }