diff --git a/processing/src/main/java/io/druid/query/groupby/epinephelinae/GroupByQueryEngineV2.java b/processing/src/main/java/io/druid/query/groupby/epinephelinae/GroupByQueryEngineV2.java
index 49f1b72917cc..e6995b333a49 100644
--- a/processing/src/main/java/io/druid/query/groupby/epinephelinae/GroupByQueryEngineV2.java
+++ b/processing/src/main/java/io/druid/query/groupby/epinephelinae/GroupByQueryEngineV2.java
@@ -36,6 +36,7 @@
 import io.druid.query.ColumnSelectorPlus;
 import io.druid.query.aggregation.AggregatorFactory;
 import io.druid.query.dimension.ColumnSelectorStrategyFactory;
+import io.druid.query.dimension.DimensionSpec;
 import io.druid.query.groupby.GroupByQuery;
 import io.druid.query.groupby.GroupByQueryConfig;
 import io.druid.query.groupby.epinephelinae.column.DictionaryBuildingStringGroupByColumnSelectorStrategy;
@@ -360,6 +361,8 @@ public Row apply(final Grouper.Entry<ByteBuffer> entry)
                 );
               }
 
+              convertRowTypesToOutputTypes(query.getDimensions(), theMap);
+
               // Add aggregations.
               for (int i = 0; i < entry.getValues().length; i++) {
                 theMap.put(query.getAggregatorSpecs().get(i).getName(), entry.getValues()[i]);
@@ -402,6 +405,34 @@ public void close()
     }
   }
 
+  private static void convertRowTypesToOutputTypes(List<DimensionSpec> dimensionSpecs, Map<String, Object> rowMap)
+  {
+    for (DimensionSpec dimSpec : dimensionSpecs) {
+      final ValueType outputType = dimSpec.getOutputType();
+      rowMap.compute(
+          dimSpec.getOutputName(),
+          (dimName, baseVal) -> {
+            switch (outputType) {
+              case STRING:
+                baseVal = baseVal == null ? "" : baseVal.toString();
+                break;
+              case LONG:
+                baseVal = DimensionHandlerUtils.convertObjectToLong(baseVal);
+                baseVal = baseVal == null ? 0L : baseVal;
+                break;
+              case FLOAT:
+                baseVal = DimensionHandlerUtils.convertObjectToFloat(baseVal);
+                baseVal = baseVal == null ? 0.f : baseVal;
+                break;
+              default:
+                throw new IAE("Unsupported type: " + outputType);
+            }
+            return baseVal;
+          }
+      );
+    }
+  }
+
   private static class GroupByEngineKeySerde implements Grouper.KeySerde<ByteBuffer>
   {
     private final int keySize;
diff --git a/processing/src/test/java/io/druid/query/groupby/GroupByQueryRunnerTest.java b/processing/src/test/java/io/druid/query/groupby/GroupByQueryRunnerTest.java
index 85feca8e6800..fadd47198cf2 100644
--- a/processing/src/test/java/io/druid/query/groupby/GroupByQueryRunnerTest.java
+++ b/processing/src/test/java/io/druid/query/groupby/GroupByQueryRunnerTest.java
@@ -30,6 +30,7 @@
 import com.google.common.collect.Maps;
 import com.google.common.collect.Ordering;
 import com.google.common.collect.Sets;
+import com.google.common.util.concurrent.ListenableFuture;
 import com.google.common.util.concurrent.MoreExecutors;
 import io.druid.collections.BlockingPool;
 import io.druid.collections.DefaultBlockingPool;
@@ -48,6 +49,7 @@
 import io.druid.js.JavaScriptConfig;
 import io.druid.query.BySegmentResultValue;
 import io.druid.query.BySegmentResultValueClass;
+import io.druid.query.ChainedExecutionQueryRunner;
 import io.druid.query.DruidProcessingConfig;
 import io.druid.query.Druids;
 import io.druid.query.FinalizeResultsQueryRunner;
@@ -58,6 +60,7 @@
 import io.druid.query.QueryRunner;
 import io.druid.query.QueryRunnerTestHelper;
 import io.druid.query.QueryToolChest;
+import io.druid.query.QueryWatcher;
 import io.druid.query.ResourceLimitExceededException;
 import io.druid.query.Result;
 import io.druid.query.aggregation.AggregatorFactory;
@@ -9129,4 +9132,58 @@ public void testSubqueryWithMultipleIntervalsInOuterQueryWithLimitPushDown()
     Iterable<Row> results = GroupByQueryRunnerTestHelper.runQuery(factory, runner, query);
     TestHelper.assertExpectedObjects(expectedResults, results, "");
   }
+
+  @Test
+  public void testTypeConversionWithMergingChainedExecutionRunner()
+  {
+    if (config.getDefaultStrategy().equals(GroupByStrategySelector.STRATEGY_V1)) {
+      expectedException.expect(UnsupportedOperationException.class);
+      expectedException.expectMessage("GroupBy v1 only supports dimensions with an outputType of STRING.");
+    }
+
+    GroupByQuery query = GroupByQuery
+        .builder()
+        .setDataSource(QueryRunnerTestHelper.dataSource)
+        .setQuerySegmentSpec(QueryRunnerTestHelper.firstToThird)
+        .setDimensions(Lists.<DimensionSpec>newArrayList(
+            new DefaultDimensionSpec("quality", "alias"),
+            new ExtractionDimensionSpec("quality", "qualityLen", ValueType.LONG, StrlenExtractionFn.instance())
+        ))
+        .setDimFilter(new SelectorDimFilter(
+            "quality",
+            "technology",
+            null
+        ))
+        .setAggregatorSpecs(
+            Arrays.asList(
+                QueryRunnerTestHelper.rowsCount,
+                new LongSumAggregatorFactory("idx", "index")
+            )
+        )
+        .setGranularity(QueryRunnerTestHelper.dayGran)
+        .build();
+
+    List<Row> expectedResults = Arrays.asList(
+        GroupByQueryRunnerTestHelper.createExpectedRow("2011-04-01", "alias", "technology", "qualityLen", 10L, "rows", 2L, "idx", 156L),
+        GroupByQueryRunnerTestHelper.createExpectedRow("2011-04-02", "alias", "technology", "qualityLen", 10L, "rows", 2L, "idx", 194L)
+    );
+
+    ChainedExecutionQueryRunner ceqr = new ChainedExecutionQueryRunner(
+        MoreExecutors.sameThreadExecutor(),
+        new QueryWatcher()
+        {
+          @Override
+          public void registerQuery(Query query, ListenableFuture future)
+          {
+            return;
+          }
+        },
+        ImmutableList.<QueryRunner<Row>>of(runner, runner)
+    );
+
+    QueryRunner<Row> mergingRunner = factory.mergeRunners(MoreExecutors.sameThreadExecutor(), ImmutableList.<QueryRunner<Row>>of(ceqr));
+
+    Iterable<Row> results = GroupByQueryRunnerTestHelper.runQuery(factory, mergingRunner, query);
+    TestHelper.assertExpectedObjects(expectedResults, results, "");
+  }
 }