diff --git a/compiler/rustc_ast_pretty/src/pp.rs b/compiler/rustc_ast_pretty/src/pp.rs
index 4f5140349c9..43a3c792d4a 100644
--- a/compiler/rustc_ast_pretty/src/pp.rs
+++ b/compiler/rustc_ast_pretty/src/pp.rs
@@ -288,12 +288,11 @@ fn scan_begin(&mut self, b: BeginToken) {
             self.left_total = 1;
             self.right_total = 1;
             self.right = self.left;
-            self.buf.truncate(1);
+            self.buf.clear();
         } else {
             self.right += 1;
-            self.buf.advance_right();
         }
-        self.buf[self.right] = BufEntry { token: Token::Begin(b), size: -self.right_total };
+        self.buf.push(BufEntry { token: Token::Begin(b), size: -self.right_total });
         self.scan_stack.push_front(self.right);
     }
 
@@ -302,8 +301,7 @@ fn scan_end(&mut self) {
             self.print_end();
         } else {
             self.right += 1;
-            self.buf.advance_right();
-            self.buf[self.right] = BufEntry { token: Token::End, size: -1 };
+            self.buf.push(BufEntry { token: Token::End, size: -1 });
             self.scan_stack.push_front(self.right);
         }
     }
@@ -329,9 +327,8 @@ fn scan_string(&mut self, s: Cow<'static, str>) {
             self.print_string(s);
         } else {
             self.right += 1;
-            self.buf.advance_right();
             let len = s.len() as isize;
-            self.buf[self.right] = BufEntry { token: Token::String(s), size: len };
+            self.buf.push(BufEntry { token: Token::String(s), size: len });
             self.right_total += len;
             self.check_stream();
         }
diff --git a/compiler/rustc_ast_pretty/src/pp/ring.rs b/compiler/rustc_ast_pretty/src/pp/ring.rs
index 7e4e353ef1f..94bb10382f8 100644
--- a/compiler/rustc_ast_pretty/src/pp/ring.rs
+++ b/compiler/rustc_ast_pretty/src/pp/ring.rs
@@ -22,6 +22,10 @@ pub fn new() -> Self {
         RingBuffer { data: VecDeque::new(), offset: 0 }
     }
 
+    pub fn push(&mut self, value: T) {
+        self.data.push_back(value);
+    }
+
     pub fn advance_right(&mut self)
     where
         T: Default,
@@ -34,6 +38,10 @@ pub fn advance_left(&mut self) {
         self.offset += 1;
     }
 
+    pub fn clear(&mut self) {
+        self.data.clear();
+    }
+
     pub fn truncate(&mut self, len: usize) {
         self.data.truncate(len);
     }