diff --git a/src/helpers.rs b/src/helpers.rs
index 7f99aa199706..a9cafd2a9e39 100644
--- a/src/helpers.rs
+++ b/src/helpers.rs
@@ -631,8 +631,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
     fn in_std(&self) -> bool {
         let this = self.eval_context_ref();
-        this.tcx.def_path(this.frame().instance.def_id()).krate
-            == this.tcx.def_path(this.tcx.lang_items().start_fn().unwrap()).krate
+        this.tcx.lang_items().start_fn().map_or(false, |start_fn| {
+            this.tcx.def_path(this.frame().instance.def_id()).krate
+                == this.tcx.def_path(start_fn).krate
+        })
     }
 }