diff --git a/autoload/flog/test.vim b/autoload/flog/test.vim
index c61d938..632670a 100644
--- a/autoload/flog/test.vim
+++ b/autoload/flog/test.vim
@@ -25,6 +25,8 @@ function! flog#test#ShowNvimBufHl() abort
       for l:virtcol in range(l:start_virtcol, l:end_virtcol)
         let l:hl_groups[l:virtcol] = l:details.hl_group
       endfor
+    else
+      echoerr 'Debug: start/end virtcol: "' .. l:start_virtcol .. '" ; "' .. l:end_vertcol .. '"' .. "\n" .. string(l:details)
     endif
   endfor