diff --git a/processing/src/main/java/io/druid/segment/incremental/OnheapIncrementalIndex.java b/processing/src/main/java/io/druid/segment/incremental/OnheapIncrementalIndex.java
index 1930463ca2e..87516bedfa7 100644
--- a/processing/src/main/java/io/druid/segment/incremental/OnheapIncrementalIndex.java
+++ b/processing/src/main/java/io/druid/segment/incremental/OnheapIncrementalIndex.java
@@ -243,6 +243,18 @@ public class OnheapIncrementalIndex extends IncrementalIndex<Aggregator>
     return concurrentGet(rowOffset)[aggOffset].get();
   }
 
+  /**
+   * Clear out maps to allow GC
+   * NOTE: This is NOT thread-safe with add... so make sure all the adding is DONE before closing
+   */
+  @Override
+  public void close()
+  {
+    super.close();
+    aggregators.clear();
+    facts.clear();
+  }
+
   private static class OnHeapDimDim implements DimDim
   {
     private final Map<String, Integer> falseIds;