gohugoio/hugo · error

invalid dictionary key

Error message

invalid dictionary key

What it means

Dictionary (collections.go:170-189) accepts keys that are either a string or a []string (the latter for nested key paths). Any other key type (int, struct, map, etc.) hits the default branch at line 187-188.

Solutions

1. Use string keys only
2. Cast scalars: {{ dictionary (string .ID) "v" }}
3. For nested paths use a slice of strings: {{ dictionary (slice "a" "b") "v" }}

Example fix

// before
{{ dictionary 1 "v" }}
// after
{{ dictionary "1" "v" }}

{{/* cast numeric/object keys to string */}}
{{ dictionary (string .ID) .Value }}

{{/* Go-side */}}
func isValidDictKey(v any) bool {
  switch v.(type) {
  case string, []string:
    return true
  }
  return false
}

When it happens

Trigger: {{ dictionary 1 "v" }} (int key), {{ dictionary .Page "v" }} (struct key), {{ dictionary .Params "v" }} (map key).

Common situations: Using a numeric ID as a key expecting coercion; passing a Page object as a key; passing a map as a key.

Related errors

• called apply using as type
• can't iterate over
• intersect does not support slices or arrays of uncomparable…
• argument must be a slice
• both limit and seq must be provided

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/9da14e1c327badf7. Report an issue: GitHub.

Appendix: source

Thrown at tpl/collections/collections.go:188

		switch v := values[i].(type) {
		case string:
			key = v
		case []string:
			for i := range len(v) - 1 {
				key = v[i]
				var m map[string]any
				v, found := dict[key]
				if found {
					m = v.(map[string]any)
				} else {
					m = make(map[string]any)
					dict[key] = m
				}
				dict = m
			}
			key = v[len(v)-1]
		default:
			return nil, errors.New("invalid dictionary key")
		}
		dict[key] = values[i+1]
	}

	return root, nil
}

// First returns the first limit items in list l.
func (ns *Namespace) First(limit any, l any) (any, error) {
	if limit == nil || l == nil {
		return nil, errors.New("both limit and seq must be provided")
	}

	limitv, err := cast.ToIntE(limit)
	if err != nil {
		return nil, err
	}

View on GitHub (pinned to 52c9bd7908)