diff --git a/src/items.rs b/src/items.rs
index a11a02be2ae..039dd1e1ae0 100644
--- a/src/items.rs
+++ b/src/items.rs
@@ -125,6 +125,7 @@ impl Rewrite for ast::Local {
 // FIXME convert to using rewrite style rather than visitor
 // FIXME format modules in this style
 #[allow(dead_code)]
+#[derive(Debug)]
 struct Item<'a> {
     unsafety: ast::Unsafe,
     abi: Cow<'static, str>,
@@ -153,6 +154,7 @@ impl<'a> Item<'a> {
     }
 }
 
+#[derive(Debug)]
 enum BodyElement<'a> {
     // Stmt(&'a ast::Stmt),
     // Field(&'a ast::Field),
@@ -174,26 +176,10 @@ pub(crate) struct FnSig<'a> {
 }
 
 impl<'a> FnSig<'a> {
-    pub(crate) fn new(
-        decl: &'a ast::FnDecl,
-        generics: &'a ast::Generics,
-        vis: ast::Visibility,
-    ) -> FnSig<'a> {
-        FnSig {
-            decl,
-            generics,
-            ext: ast::Extern::None,
-            is_async: Cow::Owned(ast::Async::No),
-            constness: ast::Const::No,
-            defaultness: ast::Defaultness::Final,
-            unsafety: ast::Unsafe::No,
-            visibility: vis,
-        }
-    }
-
     pub(crate) fn from_method_sig(
         method_sig: &'a ast::FnSig,
         generics: &'a ast::Generics,
+        visibility: ast::Visibility,
     ) -> FnSig<'a> {
         FnSig {
             unsafety: method_sig.header.unsafety,
@@ -203,7 +189,7 @@ impl<'a> FnSig<'a> {
             ext: method_sig.header.ext,
             decl: &*method_sig.decl,
             generics,
-            visibility: DEFAULT_VISIBILITY,
+            visibility,
         }
     }
 
@@ -216,9 +202,8 @@ impl<'a> FnSig<'a> {
         match *fn_kind {
             visit::FnKind::Fn(fn_ctxt, _, fn_sig, vis, _) => match fn_ctxt {
                 visit::FnCtxt::Assoc(..) => {
-                    let mut fn_sig = FnSig::from_method_sig(fn_sig, generics);
+                    let mut fn_sig = FnSig::from_method_sig(fn_sig, generics, vis.clone());
                     fn_sig.defaultness = defaultness;
-                    fn_sig.visibility = vis.clone();
                     fn_sig
                 }
                 _ => FnSig {
@@ -347,7 +332,7 @@ impl<'a> FmtVisitor<'a> {
             &context,
             indent,
             ident,
-            &FnSig::from_method_sig(sig, generics),
+            &FnSig::from_method_sig(sig, generics, DEFAULT_VISIBILITY),
             span,
             FnBraceStyle::None,
         )?;
@@ -3058,11 +3043,27 @@ impl Rewrite for ast::ForeignItem {
         let span = mk_sp(self.span.lo(), self.span.hi() - BytePos(1));
 
         let item_str = match self.kind {
-            ast::ForeignItemKind::Fn(_, ref fn_sig, ref generics, _) => rewrite_fn_base(
+            ast::ForeignItemKind::Fn(defaultness, ref fn_sig, ref generics, Some(ref body)) => {
+                let mut visitor = FmtVisitor::from_context(context);
+                visitor.block_indent = shape.indent;
+                visitor.last_pos = self.span.lo();
+                let inner_attrs = inner_attributes(&self.attrs);
+                let fn_ctxt = visit::FnCtxt::Foreign;
+                visitor.visit_fn(
+                    visit::FnKind::Fn(fn_ctxt, self.ident, &fn_sig, &self.vis, Some(body)),
+                    generics,
+                    &fn_sig.decl,
+                    self.span,
+                    defaultness,
+                    Some(&inner_attrs),
+                );
+                Some(visitor.buffer.to_owned())
+            }
+            ast::ForeignItemKind::Fn(_, ref fn_sig, ref generics, None) => rewrite_fn_base(
                 context,
                 shape.indent,
                 self.ident,
-                &FnSig::new(&fn_sig.decl, generics, self.vis.clone()),
+                &FnSig::from_method_sig(&fn_sig, generics, self.vis.clone()),
                 span,
                 FnBraceStyle::None,
             )
diff --git a/src/visitor.rs b/src/visitor.rs
index ecf72833195..3b9b0a2f967 100644
--- a/src/visitor.rs
+++ b/src/visitor.rs
@@ -370,7 +370,7 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
 
     // Note that this only gets called for function definitions. Required methods
     // on traits do not get handled here.
-    fn visit_fn(
+    pub(crate) fn visit_fn(
         &mut self,
         fk: visit::FnKind<'_>,
         generics: &ast::Generics,
diff --git a/tests/source/extern.rs b/tests/source/extern.rs
index 564c078ed2c..d0a033b1243 100644
--- a/tests/source/extern.rs
+++ b/tests/source/extern.rs
@@ -58,6 +58,20 @@ libc::c_long;
                                , mode3: *const c_char,
                                file: *mut FILE)
                               -> *mut FILE;
+
+
+       const fn foo(
+
+       ) ->
+                            *mut Bar;
+       unsafe fn foo(
+
+       ) -> *
+       mut
+       Bar;
+
+       pub(super) const fn foo() -> *mut Bar;
+       pub(crate) unsafe fn foo() -> *mut Bar;
    }
 
 extern {
diff --git a/tests/target/extern.rs b/tests/target/extern.rs
index d25dba7d1bb..44ed6d4b475 100644
--- a/tests/target/extern.rs
+++ b/tests/target/extern.rs
@@ -73,6 +73,12 @@ extern "C" {
         mode3: *const c_char,
         file: *mut FILE,
     ) -> *mut FILE;
+
+    const fn foo() -> *mut Bar;
+    unsafe fn foo() -> *mut Bar;
+
+    pub(super) const fn foo() -> *mut Bar;
+    pub(crate) unsafe fn foo() -> *mut Bar;
 }
 
 extern "C" {}
diff --git a/tests/target/issue-4313.rs b/tests/target/issue-4313.rs
new file mode 100644
index 00000000000..c390ee6ba30
--- /dev/null
+++ b/tests/target/issue-4313.rs
@@ -0,0 +1,5 @@
+extern "C" {
+    fn f() {
+        fn g() {}
+    }
+}