diff --git a/library/proc_macro/src/bridge/closure.rs b/library/proc_macro/src/bridge/closure.rs
index 524fdf53d6b..e0e688434dc 100644
--- a/library/proc_macro/src/bridge/closure.rs
+++ b/library/proc_macro/src/bridge/closure.rs
@@ -19,7 +19,7 @@ struct Env;
 impl<'a, A, R, F: FnMut(A) -> R> From<&'a mut F> for Closure<'a, A, R> {
     fn from(f: &'a mut F) -> Self {
         unsafe extern "C" fn call<A, R, F: FnMut(A) -> R>(env: *mut Env, arg: A) -> R {
-            (*(env as *mut _ as *mut F))(arg)
+            unsafe { (*(env as *mut _ as *mut F))(arg) }
         }
         Closure { call: call::<A, R, F>, env: f as *mut _ as *mut Env, _marker: PhantomData }
     }
diff --git a/library/proc_macro/src/lib.rs b/library/proc_macro/src/lib.rs
index 6611ce30a1b..d9141eab591 100644
--- a/library/proc_macro/src/lib.rs
+++ b/library/proc_macro/src/lib.rs
@@ -33,6 +33,7 @@
 #![deny(ffi_unwind_calls)]
 #![warn(rustdoc::unescaped_backticks)]
 #![warn(unreachable_pub)]
+#![deny(unsafe_op_in_unsafe_fn)]
 
 #[unstable(feature = "proc_macro_internals", issue = "27812")]
 #[doc(hidden)]