diff --git a/uk/ac/sanger/artemis/components/genebuilder/cv/ProductBox.java b/uk/ac/sanger/artemis/components/genebuilder/cv/ProductBox.java
index 483aee99d5a21b2cc7d582cd2a16bc190c7dcf53..c9983887e33ca7fa8390a2bb2f45daa9c9597056 100644
--- a/uk/ac/sanger/artemis/components/genebuilder/cv/ProductBox.java
+++ b/uk/ac/sanger/artemis/components/genebuilder/cv/ProductBox.java
@@ -185,7 +185,8 @@ class ProductBox extends AbstractCvBox
     }
     
     old = getField("evidence=", origQualifierString);
-    if(!old.equals(GoBox.evidenceCodes[2][ evidenceList.getSelectedIndex() ]))
+    if(evidenceList.getSelectedIndex() > -1 &&
+       !old.equals(GoBox.evidenceCodes[2][ evidenceList.getSelectedIndex() ]))
     {
       newQualifierString = changeField("evidence=", 
                    GoBox.evidenceCodes[2][ evidenceList.getSelectedIndex() ],