diff --git a/java/src/org/broadinstitute/sting/oneoffprojects/walkers/CNV/GCcontentIntervalWalker.java b/java/src/org/broadinstitute/sting/oneoffprojects/walkers/CNV/GCcontentIntervalWalker.java
index 8cddd0b64..0922df26d 100755
--- a/java/src/org/broadinstitute/sting/oneoffprojects/walkers/CNV/GCcontentIntervalWalker.java
+++ b/java/src/org/broadinstitute/sting/oneoffprojects/walkers/CNV/GCcontentIntervalWalker.java
@@ -45,7 +45,9 @@ import java.util.*;
 @Allows(value = {DataSource.REFERENCE})
 @Requires(value = {DataSource.REFERENCE})
 
-public class GCcontentIntervalWalker extends RodWalker<GCcounter, GCcounter> {
+@By(DataSource.REFERENCE)
+
+public class GCcontentIntervalWalker extends LocusWalker<GCcounter, GCcounter> {
     @Output
     protected PrintStream out;