diff --git a/compiler/rustc_middle/src/mir/mono.rs b/compiler/rustc_middle/src/mir/mono.rs
index ff54ec56a29..f31b343c947 100644
--- a/compiler/rustc_middle/src/mir/mono.rs
+++ b/compiler/rustc_middle/src/mir/mono.rs
@@ -334,10 +334,7 @@ impl<'tcx> CodegenUnit<'tcx> {
     }
 
     pub fn modify_size_estimate(&mut self, delta: usize) {
-        assert!(self.size_estimate.is_some());
-        if let Some(size_estimate) = self.size_estimate {
-            self.size_estimate = Some(size_estimate + delta);
-        }
+        *self.size_estimate.as_mut().unwrap() += delta;
     }
 
     pub fn contains_item(&self, item: &MonoItem<'tcx>) -> bool {