diff --git a/python/obitools3/commands/uniq.pyx b/python/obitools3/commands/uniq.pyx
index 15ff5d3..b733450 100644
--- a/python/obitools3/commands/uniq.pyx
+++ b/python/obitools3/commands/uniq.pyx
@@ -354,6 +354,9 @@ cdef uniq_sequences(View_NUC_SEQS view, View_NUC_SEQS o_view, ProgressBar pb, di
         key = mergedKeys[k]
         merged_col_name = mergedKeys_m[k]
         
+        if merged_infos[merged_col_name]['nb_elts'] == 1:
+            raise Exception("Can't merge information from a tag with only one element (e.g. one sample ; don't use -m option)")
+        
         if merged_col_name in view:
             i_col = view[merged_col_name]
         else: