diff --git a/core/mappings.vim b/core/mappings.vim
index ebd9d26..c6362c4 100644
--- a/core/mappings.vim
+++ b/core/mappings.vim
@@ -46,8 +46,10 @@ nnoremap <silent> \d :<C-U>bprevious <bar> bdelete #<CR>
 
 " Insert a blank line below or above current line (do not move the cursor),
 " see https://stackoverflow.com/a/16136133/6064933
-nnoremap <expr> oo printf('m`%so<ESC>``', v:count1)
-nnoremap <expr> OO printf('m`%sO<ESC>``', v:count1)
+nnoremap oo :echo 'Please use <lt>M-o> instead'<CR>
+nnoremap OO :echo 'Please use <lt>M-O> instead'<CR>
+nnoremap <expr> <M-o> printf('m`%so<ESC>``', v:count1)
+nnoremap <expr> <M-O> printf('m`%sO<ESC>``', v:count1)
 
 " Insert a space after current character
 nnoremap <Space><Space> a<Space><ESC>h