diff --git a/src/nvim/mapping.c b/src/nvim/mapping.c
index ab9d68f911..147985377e 100644
--- a/src/nvim/mapping.c
+++ b/src/nvim/mapping.c
@@ -2804,8 +2804,7 @@ void modify_keymap(uint64_t channel_id, Buffer buffer, bool is_unmap, String mod
     api_set_error(err, kErrorTypeException, e_nomap, 0);
     goto fail_and_free;
   case 5:
-    api_set_error(err, kErrorTypeException,
-                  "E227: mapping already exists for %s", parsed_args.lhs);
+    api_set_error(err, kErrorTypeException, e_mapping_already_exists_for_str, lhs.data);
     goto fail_and_free;
   default:
     assert(false && "Unrecognized return code!");
diff --git a/test/functional/api/keymap_spec.lua b/test/functional/api/keymap_spec.lua
index 995711507f..73dae0dd60 100644
--- a/test/functional/api/keymap_spec.lua
+++ b/test/functional/api/keymap_spec.lua
@@ -803,11 +803,17 @@ describe('nvim_set_keymap, nvim_del_keymap', function()
   it('throws appropriate error messages when setting <unique> maps', function()
     api.nvim_set_keymap('l', 'lhs', 'rhs', {})
     eq(
-      'E227: mapping already exists for lhs',
+      'E227: Mapping already exists for lhs',
       pcall_err(api.nvim_set_keymap, 'l', 'lhs', 'rhs', { unique = true })
     )
     -- different mapmode, no error should be thrown
     api.nvim_set_keymap('t', 'lhs', 'rhs', { unique = true })
+
+    api.nvim_set_keymap('n', '<tab>', 'rhs', {})
+    eq(
+      'E227: Mapping already exists for <tab>',
+      pcall_err(api.nvim_set_keymap, 'n', '<tab>', 'rhs', { unique = true })
+    )
   end)
 
   it('can set <expr> mappings whose RHS change dynamically', function()