Invalid allow-fallback value %#v, allowed values: shifted, a

Error message

Invalid allow-fallback value %#v, allowed values: shifted, ascii, none

What it means

The allow-fallback value for a map directive must be one of shifted, ascii, none (or a comma-separated list of shifted/ascii). validateAllowFallback rejects any other token when parsing the map option.

Source

Thrown at tools/config/utils.go:265

type KeyAction struct {
	Normalized_keys []string
	Name            string
	Args            string
	AllowFallback   string
}

func (self *KeyAction) String() string {
	return fmt.Sprintf("map %#v %#v %#v\n", strings.Join(self.Normalized_keys, ">"), self.Name, self.Args)
}

func validateAllowFallback(value string) error {
	if value == "" || value == "none" {
		return nil
	}
	for part := range strings.SplitSeq(value, ",") {
		part = strings.TrimSpace(part)
		if part != "shifted" && part != "ascii" {
			return fmt.Errorf("Invalid allow-fallback value %#v, allowed values: shifted, ascii, none", part)
		}
	}
	return nil
}

func ParseMap(val string) (*KeyAction, error) {
	allow_fallback := "shifted"
	for strings.HasPrefix(val, "--") {
		flag, rest, found := strings.Cut(val, " ")
		if !found {
			return nil, fmt.Errorf("No key specified after flag %s", flag)
		}
		rest = strings.TrimSpace(rest)
		if name, value, ok := strings.Cut(flag, "="); ok {
			// --flag=value form
			name = strings.ReplaceAll(name[2:], "-", "_")
			switch name {
			case "allow_fallback":

View on GitHub (pinned to 6d5d0c4406)

Solutions

Change the value to shifted, ascii, none, or a comma combination like shifted,ascii
Check spelling and case exactly
If upgrading, review changelog notes about allow-fallback semantics

Example fix

# before
map --allow-fallback=Shifted ctrl+a 1
# after
map --allow-fallback=shifted ctrl+a 1

Defensive patterns

Strategy: validation

Validate before calling

valid := map[string]bool{"shifted": true, "ascii": true, "none": true, "": true}
for _, p := range strings.Split(value, ",") {
    p = strings.TrimSpace(p)
    if !valid[p] { return fmt.Errorf("bad allow-fallback %q", p) }
}

Type guard

func isValidAllowFallback(v string) bool {
    if v == "" || v == "none" { return true }
    for _, p := range strings.Split(v, ",") {
        p = strings.TrimSpace(p)
        if p != "shifted" && p != "ascii" { return false }
    }
    return true
}

Prevention

Use exactly shifted, ascii, none in lowercase
Prefer the comma form without spaces: shifted,ascii

When it happens

Trigger: Passing --allow-fallback=xyz or `--allow-fallback xyz` to a map directive in a config file, where xyz is not shifted, ascii, none, or a comma list of those.

Common situations: Typos like 'shfted' or 'ASCII' (case-sensitive), or assuming legacy values from older kitty versions where this validation did not exist.

Related errors

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/fa2478dd8688f2dd. Report an issue: GitHub.