diff --git a/runtime/lua/vim/_core/help.lua b/runtime/lua/vim/_core/help.lua
index 87f9d462de..cc410daf17 100644
--- a/runtime/lua/vim/_core/help.lua
+++ b/runtime/lua/vim/_core/help.lua
@@ -108,7 +108,7 @@ function M.escape_subject(word)
     -- E.g. 'iCTRL-GCTRL-J' --> 'i_CTRL-G_CTRL-J'
     -- Only exception: 'CTRL-{character}'
     word = word:gsub('([^_])CTRL%-', '%1_CTRL-')
-    word = word:gsub('(CTRL%-[^{])([^_\\])', '%1_%2')
+    word = word:gsub('(CTRL%-[^{])([^-_\\])', '%1_%2')
 
     -- Skip function arguments
     -- E.g. 'abs({expr})' --> 'abs'
diff --git a/test/functional/ex_cmds/help_spec.lua b/test/functional/ex_cmds/help_spec.lua
index ffec9e50b0..7edb0556c5 100644
--- a/test/functional/ex_cmds/help_spec.lua
+++ b/test/functional/ex_cmds/help_spec.lua
@@ -130,6 +130,7 @@ describe(':help', function()
     check_tag('help <>', '*<>*')
     check_tag([[help i^x^y]], '*i_CTRL-X_CTRL-Y*')
     check_tag([[help CTRL-\_CTRL-N]], [[*CTRL-\_CTRL-N*]])
+    check_tag([[help i_CTRL-U-default]], [[*i_CTRL-U-default*]])
 
     check_tag([[exe "help i\<C-\>\<C-G>"]], [[*i_CTRL-\_CTRL-G*]])
     check_tag([[exe "help \<C-V>"]], '*CTRL-V*')