diff --git a/server/src/main/java/com/metamx/druid/query/group/GroupByQueryEngine.java b/server/src/main/java/com/metamx/druid/query/group/GroupByQueryEngine.java
index b8d13be6674..88cb5840950 100644
--- a/server/src/main/java/com/metamx/druid/query/group/GroupByQueryEngine.java
+++ b/server/src/main/java/com/metamx/druid/query/group/GroupByQueryEngine.java
@@ -236,6 +236,11 @@ public class GroupByQueryEngine
       }
     }
 
+    public int getIncrement()
+    {
+      return increment;
+    }
+
     public int[] getIncrements()
     {
       return increments;
@@ -301,11 +306,11 @@ public class GroupByQueryEngine
         return delegate.next();
       }
 
-      if (cursor.isDone()) {
+      if (unprocessedKeys == null && cursor.isDone()) {
         throw new NoSuchElementException();
       }
 
-      final PositionMaintainer positionMaintainer = new PositionMaintainer(0, sizesRequired, metricsBuffer.limit());
+      final PositionMaintainer positionMaintainer = new PositionMaintainer(0, sizesRequired, metricsBuffer.remaining());
       final RowUpdater rowUpdater = new RowUpdater(metricsBuffer, aggregators, positionMaintainer);
       if (unprocessedKeys != null) {
         for (ByteBuffer key : unprocessedKeys) {
@@ -327,6 +332,13 @@ public class GroupByQueryEngine
         cursor.advance();
       }
 
+      if (rowUpdater.getPositions().isEmpty() && unprocessedKeys != null) {
+        throw new ISE(
+            "Not enough memory to process even a single item.  Required [%,d] memory, but only have[%,d]",
+            positionMaintainer.getIncrement(), metricsBuffer.remaining()
+        );
+      }
+
       delegate = FunctionalIterator
           .create(rowUpdater.getPositions().entrySet().iterator())
           .transform(