#### Note: this error code is no longer emitted by the compiler. An intrinsic was declared without being a function. Erroneous code example: ```ignore (no longer emitted) #![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: ```ignore (no longer emitted) #![feature(intrinsics)] #![allow(internal_features)] #[rustc_intrinsic] pub unsafe fn atomic_singlethreadfence_seqcst(); // ok! fn main() { unsafe { atomic_singlethreadfence_seqcst(); } } ```