diff --git a/src/librustc_parse/parser/expr.rs b/src/librustc_parse/parser/expr.rs
index cc5e708be48..982b74adfb0 100644
--- a/src/librustc_parse/parser/expr.rs
+++ b/src/librustc_parse/parser/expr.rs
@@ -482,29 +482,8 @@ impl<'a> Parser<'a> {
                 (lo.to(span), self.mk_unary(UnOp::Deref, e))
             }
             token::BinOp(token::And) | token::AndAnd => self.parse_borrow_expr(lo)?,
-            token::Ident(..) if self.token.is_keyword(kw::Box) => {
-                self.bump();
-                let e = self.parse_prefix_expr(None);
-                let (span, e) = self.interpolated_or_expr_span(e)?;
-                let span = lo.to(span);
-                self.sess.gated_spans.gate(sym::box_syntax, span);
-                (span, ExprKind::Box(e))
-            }
-            token::Ident(..) if self.token.is_ident_named(sym::not) => {
-                // `not` is just an ordinary identifier in Rust-the-language,
-                // but as `rustc`-the-compiler, we can issue clever diagnostics
-                // for confused users who really want to say `!`
-                let token_cannot_continue_expr = |t: &Token| match t.kind {
-                    // These tokens can start an expression after `!`, but
-                    // can't continue an expression after an ident
-                    token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
-                    token::Literal(..) | token::Pound => true,
-                    _ => t.is_whole_expr(),
-                };
-                if !self.look_ahead(1, token_cannot_continue_expr) {
-                    return self.parse_dot_or_call_expr(Some(attrs));
-                }
-
+            token::Ident(..) if self.token.is_keyword(kw::Box) => self.parse_box_expr(lo)?,
+            token::Ident(..) if self.is_mistaken_not_ident_negation() => {
                 self.recover_not_expr(lo)?
             }
             _ => return self.parse_dot_or_call_expr(Some(attrs)),
@@ -512,6 +491,28 @@ impl<'a> Parser<'a> {
         return Ok(self.mk_expr(lo.to(hi), ex, attrs));
     }
 
+    /// Parse `box expr`.
+    fn parse_box_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
+        self.bump();
+        let e = self.parse_prefix_expr(None);
+        let (span, e) = self.interpolated_or_expr_span(e)?;
+        let span = lo.to(span);
+        self.sess.gated_spans.gate(sym::box_syntax, span);
+        Ok((span, ExprKind::Box(e)))
+    }
+
+    fn is_mistaken_not_ident_negation(&self) -> bool {
+        let token_cannot_continue_expr = |t: &Token| match t.kind {
+            // These tokens can start an expression after `!`, but
+            // can't continue an expression after an ident
+            token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
+            token::Literal(..) | token::Pound => true,
+            _ => t.is_whole_expr(),
+        };
+        self.token.is_ident_named(sym::not) && self.look_ahead(1, token_cannot_continue_expr)
+    }
+
+    /// Recover on `not expr` in favor of `!expr`.
     fn recover_not_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
         self.bump();
         // Emit the error ...