PHP error guide

Argument must be of type: meaning and fix

fatal type Affects: PHP 8.x Last verified:

Error summary

Validate and deliberately convert input before calling the typed function. Runtime argument type enforcement rejects the supplied value.

What it means

Validate and deliberately convert input before calling the typed function. Runtime argument type enforcement rejects the supplied value.

What the error means

This message means that runtime argument type enforcement rejects the supplied value. The exact signature distinguishes argument must be of type from a generic application failure.

Why PHP produces it

The engine or service reports “Argument must be of type” because its required precondition was not met. Validate and deliberately convert input before calling the typed function.

PHP version notes

The argument must be of type wording here is based on PHP 8.x; punctuation and exception class names can differ on older branches or vendor builds.

Most common causes

  • The immediate input or configuration reaches the specific condition: runtime argument type enforcement rejects the supplied value
  • The code path assumes the prerequisite for argument must be of type has already been satisfied.
  • For argument must be of type, development and production differ in version, extension, permissions, paths, or service configuration.
  • An earlier operation returned an unchecked value that is consumed by the line reporting argument must be of type.

Minimal examples

BAD — reproduces the problem

php 
save($_GET["id"]);

FIXED — safer pattern

php 
$id = filter_input(INPUT_GET, "id", FILTER_VALIDATE_INT);
if ($id === false || $id === null) { throw new InvalidArgumentException(); }
save($id);

Step-by-step diagnosis

  1. Copy the complete “Fatal error: Uncaught TypeError: save(): Argument #1 ($id) must be of type int, string given” text and retain the first application stack frame.
  2. Reproduce argument must be of type in the same SAPI and environment listed for this page.
  3. Before changing argument must be of type, inspect the preceding value or directive and verify its type, path, version, and permissions.
  4. Apply the narrow correction—validate and deliberately convert input before calling the typed function—then repeat the original request once.

Fixes

Correct the failing prerequisite

Validate and deliberately convert input before calling the typed function

php 
$id = filter_input(INPUT_GET, "id", FILTER_VALIDATE_INT);
if ($id === false || $id === null) { throw new InvalidArgumentException(); }
save($id);

Fail explicitly at the boundary

Validate the condition before the operation that emits argument must be of type, and log a safe diagnostic without credentials or full production paths.

Common mistakes when fixing it

  • Suppressing argument must be of type instead of correcting its upstream condition.
  • Testing argument must be of type only with the CLI binary when the failing request runs under FPM or Apache.
  • Changing a global setting for argument must be of type before confirming the site-specific effective configuration.

How to prevent it

  • Add a focused test that exercises the boundary responsible for argument must be of type.
  • Keep runtime versions, extensions, configuration, and deploy artifacts affecting argument must be of type reproducible.
  • Validate external data and service return values before they can trigger argument must be of type.

Web server / environment notes

cli, fpm, linux. The failure occurs where runtime argument type enforcement rejects the supplied value

Tags: cli,fpm,linux

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