diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 14ee083eceebe..46ef308cbf27c 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -132,6 +132,7 @@ symbols! {
         Borrow,
         Break,
         C,
+        CStr,
         CString,
         Center,
         Clone,
diff --git a/library/std/src/ffi/c_str.rs b/library/std/src/ffi/c_str.rs
index a828a57fc8fb5..2a4ef553be399 100644
--- a/library/std/src/ffi/c_str.rs
+++ b/library/std/src/ffi/c_str.rs
@@ -185,6 +185,7 @@ pub struct CString {
 ///
 /// [`&str`]: prim@str
 #[derive(Hash)]
+#[cfg_attr(not(test), rustc_diagnostic_item = "CStr")]
 #[stable(feature = "rust1", since = "1.0.0")]
 // FIXME:
 // `fn from` in `impl From<&CStr> for Box<CStr>` current implementation relies