Note: this error code is no longer emitted by the compiler.

An intrinsic was declared without being a function.

Erroneous code example:

#![feature(intrinsics)]
#![allow(internal_features)]

extern "C" {
    #[rustc_intrinsic]
    pub static atomic_singlethreadfence_seqcst: unsafe fn();
    // error: intrinsic must be a function
}

fn main() { unsafe { atomic_singlethreadfence_seqcst(); } }

An intrinsic is a function available for use in a given programming language whose implementation is handled specially by the compiler. In order to fix this error, just declare a function. Example:

#![feature(intrinsics)]
#![allow(internal_features)]

#[rustc_intrinsic]
pub unsafe fn atomic_singlethreadfence_seqcst(); // ok!

fn main() { unsafe { atomic_singlethreadfence_seqcst(); } }