diff --git a/src/items.rs b/src/items.rs
index a2c0e8e0f50..da70c819ad8 100644
--- a/src/items.rs
+++ b/src/items.rs
@@ -430,6 +430,10 @@ impl<'a> FmtVisitor<'a> {
     ) -> Option<(String, FnBraceStyle)> {
         let context = self.get_context();
 
+        if out_of_file_lines_range!(self, span) {
+            return Some((context.snippet(span).to_owned(), FnBraceStyle::None));
+        }
+
         let mut fn_brace_style = newline_for_brace(self.config, &fn_sig.generics.where_clause);
         let (result, _, force_newline_brace) =
             rewrite_fn_base(&context, indent, ident, fn_sig, span, fn_brace_style).ok()?;
diff --git a/src/visitor.rs b/src/visitor.rs
index 4072a1d8697..14f60658054 100644
--- a/src/visitor.rs
+++ b/src/visitor.rs
@@ -429,7 +429,7 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
                 FnBraceStyle::NextLine => {
                     self.push_str(&self.block_indent.to_string_with_newline(self.config))
                 }
-                _ => unreachable!(),
+                FnBraceStyle::None => {}
             }
             self.last_pos = source!(self, block.span).lo();
         } else {
diff --git a/tests/source/issue-6864.rs b/tests/source/issue-6864.rs
new file mode 100644
index 00000000000..ebdb59c1a5c
--- /dev/null
+++ b/tests/source/issue-6864.rs
@@ -0,0 +1,13 @@
+// rustfmt-file_lines: [{"file":"tests/source/issue-6864.rs","range":[10,12]}]
+
+fn messy_signature(
+a: i32,
+b: bool,
+)
+
+    {
+println!("weeeeeee");
+let x =
+a + b
+as i32;
+}
diff --git a/tests/target/issue-6864.rs b/tests/target/issue-6864.rs
new file mode 100644
index 00000000000..de5b055eb51
--- /dev/null
+++ b/tests/target/issue-6864.rs
@@ -0,0 +1,11 @@
+// rustfmt-file_lines: [{"file":"tests/source/issue-6864.rs","range":[10,12]}]
+
+fn messy_signature(
+a: i32,
+b: bool,
+)
+
+    {
+println!("weeeeeee");
+    let x = a + b as i32;
+}