diff --git a/src/testdir/test_termdebug.vim b/src/testdir/test_termdebug.vim
index 17e1d89..0acdab1 100644
--- a/src/testdir/test_termdebug.vim
+++ b/src/testdir/test_termdebug.vim
@@ -57,6 +57,8 @@
 
 packadd termdebug
 
+" should be the first test to run, since it validates the window layout with
+" win ids
 func Test_termdebug_basic()
   let bin_name = 'XTD_basic'
   let src_name = bin_name .. '.c'
@@ -620,4 +622,22 @@
   unlet g:termdebug_config
 endfunction
 
+function Test_termdebug_config_debug()
+  let s:error_message = '\[termdebug\] Termdebug already loaded'
+
+  " USER mode: No error message shall be displayed
+  packadd termdebug
+  call assert_true(execute('messages') !~ s:error_message)
+
+  " DEBUG mode: Error message shall now be displayed
+  let g:termdebug_config = {}
+  let g:termdebug_config['debug'] = 1
+  packadd termdebug
+  call assert_true(execute('messages') =~ s:error_message)
+
+  unlet g:termdebug_config
+  unlet g:termdebug_loaded
+  " Revert DEBUG mode, by reloading the plugin
+  source $VIMRUNTIME/pack/dist/opt/termdebug/plugin/termdebug.vim
+endfunction
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index 422633a..6b263ea 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    878,
+/**/
     877,
 /**/
     876,