diff --git a/compiler/rustc_mir/src/borrow_check/nll.rs b/compiler/rustc_mir/src/borrow_check/nll.rs
index a1f8df1922fc..aa428328fe92 100644
--- a/compiler/rustc_mir/src/borrow_check/nll.rs
+++ b/compiler/rustc_mir/src/borrow_check/nll.rs
@@ -294,7 +294,7 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
 
     // Solve the region constraints.
     let (closure_region_requirements, nll_errors) =
-        regioncx.solve(infcx, &body, def_id, polonius_output.clone());
+        regioncx.solve(infcx, &body, polonius_output.clone());
 
     if !nll_errors.is_empty() {
         // Suppress unhelpful extra errors in `infer_opaque_types`.
diff --git a/compiler/rustc_mir/src/borrow_check/region_infer/mod.rs b/compiler/rustc_mir/src/borrow_check/region_infer/mod.rs
index 3dc082a4413b..5492e328535e 100644
--- a/compiler/rustc_mir/src/borrow_check/region_infer/mod.rs
+++ b/compiler/rustc_mir/src/borrow_check/region_infer/mod.rs
@@ -548,9 +548,9 @@ pub(super) fn solve(
         &mut self,
         infcx: &InferCtxt<'_, 'tcx>,
         body: &Body<'tcx>,
-        mir_def_id: DefId,
         polonius_output: Option<Rc<PoloniusOutput>>,
     ) -> (Option<ClosureRegionRequirements<'tcx>>, RegionErrors<'tcx>) {
+        let mir_def_id = body.source.def_id();
         self.propagate_constraints(body, infcx.tcx);
 
         let mut errors_buffer = RegionErrors::new();