diff --git a/java/src/org/broadinstitute/sting/utils/exceptions/UserException.java b/java/src/org/broadinstitute/sting/utils/exceptions/UserException.java
index f9902035d..146bf75bd 100755
--- a/java/src/org/broadinstitute/sting/utils/exceptions/UserException.java
+++ b/java/src/org/broadinstitute/sting/utils/exceptions/UserException.java
@@ -118,7 +118,7 @@ public class UserException extends ReviewedStingException {
 
     public static class ReadMissingReadGroup extends MalformedBam {
         public ReadMissingReadGroup(SAMRecord read) {
-            super(read, String.format("Read %s is missing the read group, which is required by the GATK", read.getReadName()));
+            super(read, String.format("Read %s is either missing the read group or its read group is not defined in the BAM header, both of which are required by the GATK", read.getReadName()));
         }
     }