diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index d7e4caa..c93562b 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -445,9 +445,12 @@
   " Remove default mappings
   imapclear
 
-  inoremap <C-M> CtrlM
+  " reset 'isident' to check it isn't used
+  set isident=
+  inoremap <C-m> CtrlM
   inoremap <A-S> AltS
   inoremap <S-/> ShiftSlash
+  set isident&
   call assert_equal([
 	\ 'i  <S-/>       * ShiftSlash',
 	\ 'i  <M-S>       * AltS',