diff --git a/src/tools/rustfmt/src/items.rs b/src/tools/rustfmt/src/items.rs
index 1aa85ce2ce55..90466b0b1110 100644
--- a/src/tools/rustfmt/src/items.rs
+++ b/src/tools/rustfmt/src/items.rs
@@ -319,12 +319,13 @@ impl<'a> FnSig<'a> {
         method_sig: &'a ast::FnSig,
         generics: &'a ast::Generics,
         visibility: &'a ast::Visibility,
+        defaultness: ast::Defaultness,
     ) -> FnSig<'a> {
         FnSig {
             safety: method_sig.header.safety,
             coroutine_kind: Cow::Borrowed(&method_sig.header.coroutine_kind),
             constness: method_sig.header.constness,
-            defaultness: ast::Defaultness::Final,
+            defaultness,
             ext: method_sig.header.ext,
             decl: &*method_sig.decl,
             generics,
@@ -339,9 +340,7 @@ impl<'a> FnSig<'a> {
     ) -> FnSig<'a> {
         match *fn_kind {
             visit::FnKind::Fn(visit::FnCtxt::Assoc(..), vis, ast::Fn { sig, generics, .. }) => {
-                let mut fn_sig = FnSig::from_method_sig(sig, generics, vis);
-                fn_sig.defaultness = defaultness;
-                fn_sig
+                FnSig::from_method_sig(sig, generics, vis, defaultness)
             }
             visit::FnKind::Fn(_, vis, ast::Fn { sig, generics, .. }) => FnSig {
                 decl,
@@ -459,6 +458,7 @@ impl<'a> FmtVisitor<'a> {
         sig: &ast::FnSig,
         vis: &ast::Visibility,
         generics: &ast::Generics,
+        defaultness: ast::Defaultness,
         span: Span,
     ) -> RewriteResult {
         // Drop semicolon or it will be interpreted as comment.
@@ -469,7 +469,7 @@ impl<'a> FmtVisitor<'a> {
             &context,
             indent,
             ident,
-            &FnSig::from_method_sig(sig, generics, vis),
+            &FnSig::from_method_sig(sig, generics, vis, defaultness),
             span,
             FnBraceStyle::None,
         )?;
@@ -3495,7 +3495,7 @@ impl Rewrite for ast::ForeignItem {
                         context,
                         shape.indent,
                         ident,
-                        &FnSig::from_method_sig(sig, generics, &self.vis),
+                        &FnSig::from_method_sig(sig, generics, &self.vis, defaultness),
                         span,
                         FnBraceStyle::None,
                     )
diff --git a/src/tools/rustfmt/src/utils.rs b/src/tools/rustfmt/src/utils.rs
index 3a2975024a33..b676803379f7 100644
--- a/src/tools/rustfmt/src/utils.rs
+++ b/src/tools/rustfmt/src/utils.rs
@@ -102,8 +102,9 @@ pub(crate) fn format_constness_right(constness: ast::Const) -> &'static str {
 #[inline]
 pub(crate) fn format_defaultness(defaultness: ast::Defaultness) -> &'static str {
     match defaultness {
+        ast::Defaultness::Implicit => "",
         ast::Defaultness::Default(..) => "default ",
-        ast::Defaultness::Final => "",
+        ast::Defaultness::Final(..) => "final ",
     }
 }
 
diff --git a/src/tools/rustfmt/src/visitor.rs b/src/tools/rustfmt/src/visitor.rs
index 8abcba121e58..742caefc7cc5 100644
--- a/src/tools/rustfmt/src/visitor.rs
+++ b/src/tools/rustfmt/src/visitor.rs
@@ -583,7 +583,15 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
                     } else {
                         let indent = self.block_indent;
                         let rewrite = self
-                            .rewrite_required_fn(indent, ident, sig, &item.vis, generics, item.span)
+                            .rewrite_required_fn(
+                                indent,
+                                ident,
+                                sig,
+                                &item.vis,
+                                generics,
+                                defaultness,
+                                item.span,
+                            )
                             .ok();
                         self.push_rewrite(item.span, rewrite);
                     }
@@ -686,7 +694,15 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
                 } else {
                     let indent = self.block_indent;
                     let rewrite = self
-                        .rewrite_required_fn(indent, fn_kind.ident, sig, &ai.vis, generics, ai.span)
+                        .rewrite_required_fn(
+                            indent,
+                            fn_kind.ident,
+                            sig,
+                            &ai.vis,
+                            generics,
+                            defaultness,
+                            ai.span,
+                        )
                         .ok();
                     self.push_rewrite(ai.span, rewrite);
                 }
diff --git a/src/tools/rustfmt/tests/target/final-kw.rs b/src/tools/rustfmt/tests/target/final-kw.rs
new file mode 100644
index 000000000000..d68b6908d76a
--- /dev/null
+++ b/src/tools/rustfmt/tests/target/final-kw.rs
@@ -0,0 +1,5 @@
+trait Foo {
+    final fn final_() {}
+
+    fn not_final() {}
+}