# Error code E0133

Unsafe code was used outside of an unsafe function or block.

Erroneous code example:

    unsafe fn f() { return; } // This is the unsafe code

    fn main() {
        f(); // error: call to unsafe function requires unsafe function or block
    }

Using unsafe functionality is potentially dangerous and disallowed by safety checks. Examples:

- Dereferencing raw pointers
- Calling functions via FFI
- Calling functions marked unsafe

These safety checks can be relaxed for a section of the code by wrapping the unsafe instructions with an `unsafe` block. For instance:

    unsafe fn f() { return; }

    fn main() {
        unsafe { f(); } // ok!
    }

See the unsafe section of the Book for more details.