What causes "'increment' must not be 0" in gohugoio/hugo?

Pass a non-zero integer increment: `{{ seq 1 2 9 }}`.

'increment' must not be 0

Error message

'increment' must not be 0

What it means

In the three-argument form of `seq` (FIRST INCREMENT LAST), the middle argument is the step. A zero increment would loop forever, so Hugo rejects it explicitly before computing the sequence size.

Source

Thrown at tpl/collections/collections.go:461

		last = first
		if last == 0 {
			return []int{}, nil
		} else if last > 0 {
			first = 1
		} else {
			first = -1
			inc = -1
		}
	} else if len(intArgs) == 2 {
		last = intArgs[1]
		if last < first {
			inc = -1
		}
	} else {
		inc = intArgs[1]
		last = intArgs[2]
		if inc == 0 {
			return nil, errors.New("'increment' must not be 0")
		}
		if first < last && inc < 0 {
			return nil, errors.New("'increment' must be > 0")
		}
		if first > last && inc > 0 {
			return nil, errors.New("'increment' must be < 0")
		}
	}

	// sanity check
	if last < -maxSeqSize {
		return nil, errSeqSizeExceedsLimit
	}
	size := ((last - first) / inc) + 1

	// sanity check
	if size <= 0 || size > maxSeqSize {
		return nil, errSeqSizeExceedsLimit

View on GitHub ↗ (pinned to 8a468df065)

Solutions

Pass a non-zero integer increment: `{{ seq 1 2 9 }}`.
Check argument order — the increment is the second of three arguments.
If the step comes from a variable, default it: `{{ $inc := default 1 .Params.step }}`.

Example fix

<!-- before -->
{{ seq 1 0 10 }}
<!-- after -->
{{ seq 1 1 10 }}

Defensive patterns

Strategy: validation

Validate before calling

{{ if eq $increment 0 }}
  {{ errorf "seq increment must be non-zero" }}
{{ else }}
  {{ range seq $first $increment $last }}...{{ end }}
{{ end }}

Prevention

Never pass 0 as the middle (increment) argument to the 3-arg seq form.
If the increment comes from site params, apply `default 1` and reject zero explicitly.
Watch integer truncation: a computed step like `div 1 2` is 0 in integer math.

When it happens

Trigger: `{{ seq 1 0 10 }}` — three arguments with the second equal to 0, or an increment variable that casts to 0 (e.g. a non-numeric string cast via `cast.ToIntSlice`).

Common situations: Increment sourced from front matter or site params that is unset or a string like "0.5" (which truncates to 0); mixing up the argument order (FIRST INCREMENT LAST, not FIRST LAST STEP).

Related errors

AI-assisted analysis of gohugoio/hugo@8a468df065 (2026-07-31). Data as JSON: /data/errors/fb7df680a7499257.json. Report an issue: GitHub ↗.