diff --git a/processing/src/main/java/io/druid/segment/incremental/IncrementalIndexStorageAdapter.java b/processing/src/main/java/io/druid/segment/incremental/IncrementalIndexStorageAdapter.java
index df47c2574ca..76cf0774861 100644
--- a/processing/src/main/java/io/druid/segment/incremental/IncrementalIndexStorageAdapter.java
+++ b/processing/src/main/java/io/druid/segment/incremental/IncrementalIndexStorageAdapter.java
@@ -420,7 +420,11 @@ public class IncrementalIndexStorageAdapter implements StorageAdapter
                     @Override
                     public Object get()
                     {
-                      final String[] dimVals = currEntry.getKey().getDims()[dimensionIndex];
+                      final String[][] dims = currEntry.getKey().getDims();
+                      if(dimensionIndex >= dims.length) {
+                        return null;
+                      }
+                      final String[] dimVals = dims[dimensionIndex];
                       if (dimVals.length == 1) {
                         return dimVals[0];
                       }
diff --git a/processing/src/test/java/io/druid/segment/incremental/IncrementalIndexStorageAdapterTest.java b/processing/src/test/java/io/druid/segment/incremental/IncrementalIndexStorageAdapterTest.java
index 1ce05305b5d..7f17d7fc2e9 100644
--- a/processing/src/test/java/io/druid/segment/incremental/IncrementalIndexStorageAdapterTest.java
+++ b/processing/src/test/java/io/druid/segment/incremental/IncrementalIndexStorageAdapterTest.java
@@ -34,6 +34,7 @@ import io.druid.granularity.QueryGranularity;
 import io.druid.query.Result;
 import io.druid.query.aggregation.AggregatorFactory;
 import io.druid.query.aggregation.CountAggregatorFactory;
+import io.druid.query.aggregation.JavaScriptAggregatorFactory;
 import io.druid.query.aggregation.LongSumAggregatorFactory;
 import io.druid.query.filter.DimFilters;
 import io.druid.query.groupby.GroupByQuery;
@@ -52,6 +53,7 @@ import org.junit.Test;
 
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
+import java.util.Arrays;
 
 /**
  */
@@ -79,26 +81,7 @@ public class IncrementalIndexStorageAdapterTest
         )
     );
 
-    GroupByQueryEngine engine = new GroupByQueryEngine(
-        Suppliers.<GroupByQueryConfig>ofInstance(new GroupByQueryConfig()
-        {
-          @Override
-          public int getMaxIntermediateRows()
-          {
-            return 5;
-          }
-        }),
-        new StupidPool(
-            new Supplier<ByteBuffer>()
-            {
-              @Override
-              public ByteBuffer get()
-              {
-                return ByteBuffer.allocate(50000);
-              }
-            }
-        )
-    );
+    GroupByQueryEngine engine = makeGroupByQueryEngine();
 
     final Sequence<Row> rows = engine.process(
         GroupByQuery.builder()
@@ -123,6 +106,93 @@ public class IncrementalIndexStorageAdapterTest
     Assert.assertEquals(ImmutableMap.of("sally", "bo", "cnt", 1l), row.getEvent());
   }
 
+  @Test
+  public void testObjectColumnSelectorOnVaryingColumnSchema() throws Exception
+  {
+    IncrementalIndex index = new IncrementalIndex(
+        0, QueryGranularity.MINUTE, new AggregatorFactory[]{new CountAggregatorFactory("cnt")}
+    );
+
+    index.add(
+        new MapBasedInputRow(
+            new DateTime("2014-09-01T00:00:00"),
+            Lists.newArrayList("billy"),
+            ImmutableMap.<String, Object>of("billy", "hi")
+        )
+    );
+    index.add(
+        new MapBasedInputRow(
+            new DateTime("2014-09-01T01:00:00"),
+            Lists.newArrayList("billy", "sally"),
+            ImmutableMap.<String, Object>of(
+                "billy", "hip",
+                "sally", "hop"
+            )
+        )
+    );
+
+    GroupByQueryEngine engine = makeGroupByQueryEngine();
+
+    final Sequence<Row> rows = engine.process(
+        GroupByQuery.builder()
+                    .setDataSource("test")
+                    .setGranularity(QueryGranularity.ALL)
+                    .setInterval(new Interval(0, new DateTime().getMillis()))
+                    .addDimension("billy")
+                    .addDimension("sally")
+                    .addAggregator(
+                        new LongSumAggregatorFactory("cnt", "cnt")
+                    )
+                    .addAggregator(
+                        new JavaScriptAggregatorFactory(
+                            "fieldLength",
+                            Arrays.asList("sally", "billy"),
+                            "function(current, s, b) { return current + (s == null ? 0 : s.length) + (b == null ? 0 : b.length); }",
+                            "function() { return 0; }",
+                            "function(a,b) { return a + b; }"
+                        )
+                    )
+                    .build(),
+        new IncrementalIndexStorageAdapter(index)
+    );
+
+    final ArrayList<Row> results = Sequences.toList(rows, Lists.<Row>newArrayList());
+
+    Assert.assertEquals(2, results.size());
+
+    MapBasedRow row = (MapBasedRow) results.get(0);
+    Assert.assertEquals(ImmutableMap.of("billy", "hi", "cnt", 1l, "fieldLength", 2.0), row.getEvent());
+
+    row = (MapBasedRow) results.get(1);
+    Assert.assertEquals(ImmutableMap.of("billy", "hip", "sally", "hop", "cnt", 1l, "fieldLength", 6.0), row.getEvent());
+  }
+
+  private static GroupByQueryEngine makeGroupByQueryEngine()
+  {
+    return new GroupByQueryEngine(
+          Suppliers.<GroupByQueryConfig>ofInstance(
+              new GroupByQueryConfig()
+              {
+                @Override
+                public int getMaxIntermediateRows()
+                {
+                  return 5;
+                }
+              }
+          ),
+          new StupidPool(
+              new Supplier<ByteBuffer>()
+              {
+                @Override
+                public ByteBuffer get()
+                {
+                  return ByteBuffer.allocate(50000);
+                }
+              }
+          )
+      );
+  }
+
   @Test
   public void testResetSanity() {
     IncrementalIndex index = new IncrementalIndex(
@@ -236,60 +306,41 @@ public class IncrementalIndexStorageAdapterTest
          0, QueryGranularity.MINUTE, new AggregatorFactory[]{new CountAggregatorFactory("cnt")}
      );
 
-     index.add(
-         new MapBasedInputRow(
-             new DateTime().minus(1).getMillis(),
-             Lists.newArrayList("billy"),
-             ImmutableMap.<String, Object>of("billy", "hi")
-         )
-     );
-     index.add(
-         new MapBasedInputRow(
-             new DateTime().minus(1).getMillis(),
-             Lists.newArrayList("sally"),
-             ImmutableMap.<String, Object>of("sally", "bo")
-         )
-     );
+    index.add(
+        new MapBasedInputRow(
+            new DateTime().minus(1).getMillis(),
+            Lists.newArrayList("billy"),
+            ImmutableMap.<String, Object>of("billy", "hi")
+        )
+    );
+    index.add(
+        new MapBasedInputRow(
+            new DateTime().minus(1).getMillis(),
+            Lists.newArrayList("sally"),
+            ImmutableMap.<String, Object>of("sally", "bo")
+        )
+    );
 
-     GroupByQueryEngine engine = new GroupByQueryEngine(
-         Suppliers.<GroupByQueryConfig>ofInstance(new GroupByQueryConfig()
-         {
-           @Override
-           public int getMaxIntermediateRows()
-           {
-             return 5;
-           }
-         }),
-         new StupidPool<ByteBuffer>(
-             new Supplier<ByteBuffer>()
-             {
-               @Override
-               public ByteBuffer get()
-               {
-                 return ByteBuffer.allocate(50000);
-               }
-             }
-         )
-     );
+    GroupByQueryEngine engine = makeGroupByQueryEngine();
 
-     final Sequence<Row> rows = engine.process(
-         GroupByQuery.builder()
-                     .setDataSource("test")
-                     .setGranularity(QueryGranularity.ALL)
-                     .setInterval(new Interval(0, new DateTime().getMillis()))
-                     .addDimension("billy")
-                     .addDimension("sally")
-                     .addAggregator(new LongSumAggregatorFactory("cnt", "cnt"))
-                     .setDimFilter(DimFilters.dimEquals("sally", (String) null))
-                     .build(),
-         new IncrementalIndexStorageAdapter(index)
-     );
+    final Sequence<Row> rows = engine.process(
+        GroupByQuery.builder()
+                    .setDataSource("test")
+                    .setGranularity(QueryGranularity.ALL)
+                    .setInterval(new Interval(0, new DateTime().getMillis()))
+                    .addDimension("billy")
+                    .addDimension("sally")
+                    .addAggregator(new LongSumAggregatorFactory("cnt", "cnt"))
+                    .setDimFilter(DimFilters.dimEquals("sally", (String) null))
+                    .build(),
+        new IncrementalIndexStorageAdapter(index)
+    );
 
-     final ArrayList<Row> results = Sequences.toList(rows, Lists.<Row>newArrayList());
+    final ArrayList<Row> results = Sequences.toList(rows, Lists.<Row>newArrayList());
 
-     Assert.assertEquals(1, results.size());
+    Assert.assertEquals(1, results.size());
 
-     MapBasedRow row = (MapBasedRow) results.get(0);
-     Assert.assertEquals(ImmutableMap.of("billy", "hi", "cnt", 1l), row.getEvent());
-   }
+    MapBasedRow row = (MapBasedRow) results.get(0);
+    Assert.assertEquals(ImmutableMap.of("billy", "hi", "cnt", 1l), row.getEvent());
+  }
 }