diff --git a/orthofinder/scripts/blast_file_processor.py b/orthofinder/scripts/blast_file_processor.py
index d28af715ce5664acc7525d35515c4f03fca8c09d..f882c1a1f07376ac6ab00de8f63a9e2c592a8453 100644
--- a/orthofinder/scripts/blast_file_processor.py
+++ b/orthofinder/scripts/blast_file_processor.py
@@ -142,7 +142,7 @@ def WriteNormalizedBlastFile(blastDir_list, B, iSpecies, jSpecies, sep = "_", qD
                     newscore = B[sequence1ID, sequence2ID]
                     row.append(newscore)
                 except IndexError as e:
-                    sys.stderr.write("\nERROR: Matrix index : %s \n" % e)
+                    sys.stderr.write("\nERROR: Matrix index on Blast species %d %d, sequences B[%d, %d] : %s \n" % (iSpeciesOpen, jSpeciesOpen, sequence1ID, sequence2ID, e))
                     pass
                 blastwriter.writerow(row)
             tempfile.flush()