PHP TypeError — What It Means & How to Fix It

What Does This Error Mean?

A TypeError is thrown when a function receives an argument of the wrong data type, or when it returns a value of the wrong type. This became much more common in PHP 7 and 8 because modern PHP lets you declare exactly what types functions accept and return. For example, if a function expects an integer but you pass a string, PHP throws a TypeError.

Affected Models

PHP 7.x
PHP 8.x

Common Causes

Passing a string to a function that declares an integer type hint: function add(int $a, int $b)
Returning the wrong type from a function that has a return type declaration
Passing null to a function parameter that is not declared as nullable
Using strict_types=1 at the top of a file, which turns PHP's automatic type conversion off
An array being passed where an object is expected, or vice versa

How to Fix It

Read the error message carefully. It tells you exactly which function was called, what type it expected, and what type it received.

Example: 'Argument 1 passed to multiply() must be of the type int, string given'. The fix is clear from the message.
Cast the value to the correct type before passing it: (int)$value, (float)$value, (string)$value.

Example: add((int)$userInput, 5); — this converts the user input to an integer before passing it.
If null is a valid value for the parameter, declare it nullable: function save(?string $name) — the ? makes it nullable.

Without the ?, passing null will throw a TypeError in PHP 8 strict mode.
If you are using declare(strict_types=1), PHP will not automatically convert types for you. You must pass exactly the right type.

Without strict_types, PHP converts '5' (string) to 5 (int) automatically. With it, the conversion does not happen and a TypeError is thrown.
If you are writing the function, consider using union types (PHP 8) to accept multiple types: function save(int|string $id).

Union types allow a parameter to accept more than one type, which is more flexible.

When to Call a Professional

TypeErrors are a normal part of modern PHP development. They are design-time errors that a PHP developer can fix by correcting the types being passed or making function signatures more flexible. If you encounter them in a third-party library, report them as bugs to that project.

Frequently Asked Questions

Did TypeErrors exist in PHP 5?

Not in the same way. PHP 5 had type hints for objects and arrays, but it did not throw TypeErrors for scalar types like int, string, and float. PHP 7 introduced scalar type hints and TypeErrors for them. PHP 8 made the type system even stricter.

What is strict_types in PHP?

Adding 'declare(strict_types=1);' at the very top of a PHP file turns off PHP's automatic type coercion. Without it, PHP converts '5' to 5 automatically. With it, passing the wrong type always throws a TypeError. It makes your code more predictable and easier to debug.

Is a TypeError catchable?

Yes. You can wrap the call in a try/catch block and catch TypeError. try { result = divide($a, $b); } catch (TypeError $e) { echo 'Invalid input type'; } This lets you handle type problems gracefully without crashing the whole script.