diff --git a/uk/ac/sanger/artemis/components/alignment/CoveragePanel.java b/uk/ac/sanger/artemis/components/alignment/CoveragePanel.java
index 0e0c3bb1c712e9cc550db00fea2d8d70564e0bf9..19b5188d970458a9b95281f6cdab966a66beacff 100644
--- a/uk/ac/sanger/artemis/components/alignment/CoveragePanel.java
+++ b/uk/ac/sanger/artemis/components/alignment/CoveragePanel.java
@@ -473,6 +473,8 @@ import net.sf.samtools.SAMRecord;
      */
     public String getToolTipText(int ypos)
     {
+      if(heatPlots == null)
+        return null;
       for(HeatMapLn h: heatPlots)
       {
         if(ypos > h.yTop && ypos < h.yBtm)