diff --git a/java/src/org/broadinstitute/sting/gatk/walkers/LocusWindowWalker.java b/java/src/org/broadinstitute/sting/gatk/walkers/LocusWindowWalker.java
index ba0ec2b5d..2d4f85e31 100755
--- a/java/src/org/broadinstitute/sting/gatk/walkers/LocusWindowWalker.java
+++ b/java/src/org/broadinstitute/sting/gatk/walkers/LocusWindowWalker.java
@@ -12,6 +12,7 @@ import net.sf.samtools.SAMRecord;
  * Time: 2:52:28 PM
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+@Requires({DataSource.READS,DataSource.REFERENCE})
 public abstract class LocusWindowWalker<MapType, ReduceType> extends Walker<MapType, ReduceType> {
     // Do we actually want to operate on the context?
     public boolean filter(RefMetaDataTracker tracker, String ref, LocusContext context) {