1 files changed, 9 insertions, 7 deletions
diff --git a/src/tools/clippy/clippy_lints/src/mut_mut.rs b/src/tools/clippy/clippy_lints/src/mut_mut.rs
index cb16f0004..bc90e131b 100644
--- a/src/tools/clippy/clippy_lints/src/mut_mut.rs
+++ b/src/tools/clippy/clippy_lints/src/mut_mut.rs
@@ -68,13 +68,15 @@ impl<'a, 'tcx> intravisit::Visitor<'tcx> for MutVisitor<'a, 'tcx> {
                     expr.span,
                     "generally you want to avoid `&mut &mut _` if possible",
                 );
-            } else if let ty::Ref(_, _, hir::Mutability::Mut) = self.cx.typeck_results().expr_ty(e).kind() {
-                span_lint(
-                    self.cx,
-                    MUT_MUT,
-                    expr.span,
-                    "this expression mutably borrows a mutable reference. Consider reborrowing",
-                );
+            } else if let ty::Ref(_, ty, hir::Mutability::Mut) = self.cx.typeck_results().expr_ty(e).kind() {
+                if ty.peel_refs().is_sized(self.cx.tcx, self.cx.param_env) {
+                    span_lint(
+                        self.cx,
+                        MUT_MUT,
+                        expr.span,
+                        "this expression mutably borrows a mutable reference. Consider reborrowing",
+                    );
+                }
             }
         }
     }