diff --git a/hbs2-git3/lib/HBS2/Git3/State/Index.hs b/hbs2-git3/lib/HBS2/Git3/State/Index.hs
index 5f7dc00b..9904448e 100644
--- a/hbs2-git3/lib/HBS2/Git3/State/Index.hs
+++ b/hbs2-git3/lib/HBS2/Git3/State/Index.hs
@@ -97,6 +97,8 @@ mergeSortedFilesN :: forall m . MonadUnliftIO m
 
 mergeSortedFilesN _ [] out  = rm out
 
+mergeSortedFilesN _ [_] out  = rm out
+
 mergeSortedFilesN getKey inputFiles outFile = do
 
   mmaped <- for inputFiles $ \fn -> do