diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index c0fec0cf565..1e4d3ba47f4 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -1471,7 +1471,7 @@ pub enum ExprKind {
     InlineAsm(P<InlineAsm>),
 
     /// Output of the `offset_of!()` macro.
-    OffsetOf(P<Ty>, Vec<Ident>),
+    OffsetOf(P<Ty>, P<[Ident]>),
 
     /// A macro invocation; pre-expansion.
     MacCall(P<MacCall>),
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 7603bebb178..99f1f4bd968 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -1458,7 +1458,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
         ExprKind::FormatArgs(fmt) => vis.visit_format_args(fmt),
         ExprKind::OffsetOf(container, fields) => {
             vis.visit_ty(container);
-            for field in fields {
+            for field in fields.iter_mut() {
                 vis.visit_ident(field);
             }
         }
diff --git a/compiler/rustc_builtin_macros/src/offset_of.rs b/compiler/rustc_builtin_macros/src/offset_of.rs
index f5c04015340..0ef3e000e41 100644
--- a/compiler/rustc_builtin_macros/src/offset_of.rs
+++ b/compiler/rustc_builtin_macros/src/offset_of.rs
@@ -41,7 +41,7 @@ fn parse_args<'a>(
     cx: &mut ExtCtxt<'a>,
     sp: Span,
     tts: TokenStream,
-) -> PResult<'a, (P<ast::Ty>, Vec<Ident>)> {
+) -> PResult<'a, (P<ast::Ty>, P<[Ident]>)> {
     let mut p = cx.new_parser_from_tts(tts);
 
     let container = p.parse_ty()?;
@@ -71,7 +71,7 @@ fn parse_args<'a>(
         break;
     }
 
-    Ok((container, fields))
+    Ok((container, fields.into()))
 }
 
 pub fn expand_offset_of<'cx>(