diff --git a/processing/src/main/java/io/druid/segment/incremental/IncrementalIndexAdapter.java b/processing/src/main/java/io/druid/segment/incremental/IncrementalIndexAdapter.java
index d9c64f84554..02406bd9b22 100644
--- a/processing/src/main/java/io/druid/segment/incremental/IncrementalIndexAdapter.java
+++ b/processing/src/main/java/io/druid/segment/incremental/IncrementalIndexAdapter.java
@@ -156,45 +156,50 @@ public class IncrementalIndexAdapter implements IndexableAdapter
   public Indexed<String> getDimValueLookup(String dimension)
   {
     final IncrementalIndex.DimDim dimDim = index.getDimensionValues(dimension);
-    if (hasNullValueDimensions.contains(dimension)
-        && !dimDim.contains(null))
-    {
-      dimDim.add(null);
+
+    if (dimDim != null) {
+      if (hasNullValueDimensions.contains(dimension)
+          && !dimDim.contains(null))
+      {
+        dimDim.add(null);
+      }
+      dimDim.sort();
+
+      return new Indexed<String>()
+      {
+        @Override
+        public Class<? extends String> getClazz()
+        {
+          return String.class;
+        }
+
+        @Override
+        public int size()
+        {
+          return dimDim.size();
+        }
+
+        @Override
+        public String get(int index)
+        {
+          return dimDim.getSortedValue(index);
+        }
+
+        @Override
+        public int indexOf(String value)
+        {
+          return dimDim.getSortedId(value);
+        }
+
+        @Override
+        public Iterator<String> iterator()
+        {
+          return IndexedIterable.create(this).iterator();
+        }
+      };
+    } else {
+      return null;
     }
-    dimDim.sort();
-
-    return new Indexed<String>()
-    {
-      @Override
-      public Class<? extends String> getClazz()
-      {
-        return String.class;
-      }
-
-      @Override
-      public int size()
-      {
-        return dimDim.size();
-      }
-
-      @Override
-      public String get(int index)
-      {
-        return dimDim.getSortedValue(index);
-      }
-
-      @Override
-      public int indexOf(String value)
-      {
-        return dimDim.getSortedId(value);
-      }
-
-      @Override
-      public Iterator<String> iterator()
-      {
-        return IndexedIterable.create(this).iterator();
-      }
-    };
   }
 
   @Override
diff --git a/processing/src/test/java/io/druid/segment/IndexMergerTest.java b/processing/src/test/java/io/druid/segment/IndexMergerTest.java
index cea20687b1a..716303a72ee 100644
--- a/processing/src/test/java/io/druid/segment/IndexMergerTest.java
+++ b/processing/src/test/java/io/druid/segment/IndexMergerTest.java
@@ -26,6 +26,7 @@ import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Sets;
+import com.metamx.collections.bitmap.RoaringBitmapFactory;
 import io.druid.data.input.MapBasedInputRow;
 import io.druid.data.input.impl.DimensionsSpec;
 import io.druid.granularity.QueryGranularity;
@@ -44,6 +45,9 @@ import io.druid.segment.incremental.IncrementalIndex;
 import io.druid.segment.incremental.IncrementalIndexAdapter;
 import io.druid.segment.incremental.IncrementalIndexSchema;
 import io.druid.segment.incremental.OnheapIncrementalIndex;
+import org.joda.time.DateTime;
+import io.druid.segment.incremental.IndexSizeExceededException;
+import org.joda.time.Interval;
 import org.junit.Assert;
 import org.junit.Rule;
 import org.junit.Test;
@@ -53,6 +57,7 @@ import org.junit.runners.Parameterized;
 
 import javax.annotation.Nullable;
 import java.io.File;
+import java.io.IOException;
 import java.lang.reflect.Field;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -1428,6 +1433,42 @@ public class IndexMergerTest
 
   }
 
+  public void testMismatchedDimensions() throws IOException, IndexSizeExceededException
+  {
+    IncrementalIndex index1 = IncrementalIndexTest.createIndex(new AggregatorFactory[]{
+        new LongSumAggregatorFactory("A", "A")
+    });
+    index1.add(new MapBasedInputRow(1L, Lists.newArrayList("d1", "d2"), ImmutableMap.<String, Object>of("d1", "a", "d2", "z", "A", 1)));
+    closer.closeLater(index1);
+
+    IncrementalIndex index2 = IncrementalIndexTest.createIndex(new AggregatorFactory[]{
+        new LongSumAggregatorFactory("A", "A"),
+        new LongSumAggregatorFactory("C", "C")
+    });
+    index2.add(new MapBasedInputRow(1l, Lists.newArrayList("d2"), ImmutableMap.<String, Object>of("d2", "z", "A", 2, "C", 100)));
+    closer.closeLater(index2);
+
+    Interval interval = new Interval(0, new DateTime().getMillis());
+    RoaringBitmapFactory factory = new RoaringBitmapFactory();
+    ArrayList<IndexableAdapter> toMerge = Lists.<IndexableAdapter>newArrayList(
+        new IncrementalIndexAdapter(interval, index1, factory),
+        new IncrementalIndexAdapter(interval, index2, factory)
+    );
+
+    final File tmpDirMerged = temporaryFolder.newFolder();
+
+    INDEX_MERGER.merge(
+        toMerge,
+        new AggregatorFactory[] {
+            new LongSumAggregatorFactory("A", "A"),
+            new LongSumAggregatorFactory("C", "C"),
+        },
+        tmpDirMerged,
+        indexSpec
+    );
+
+  }
+
   private IncrementalIndex getIndexD3() throws Exception
   {
     IncrementalIndex toPersist1 = new OnheapIncrementalIndex(