diff --git a/src/driver.rs b/src/driver.rs
index d5143e143..94af21568 100644
--- a/src/driver.rs
+++ b/src/driver.rs
@@ -83,7 +83,7 @@ impl rustc_driver::Callbacks for ClippyCallbacks {
         // run on the unoptimized MIR. On the other hand this results in some false negatives. If
         // MIR passes can be enabled / disabled separately, we should figure out, what passes to
         // use for Clippy.
-        config.opts.debugging_opts.mir_opt_level = 0;
+        config.opts.debugging_opts.mir_opt_level = Some(0);
     }
 }