diff --git a/compiler/rustc_middle/src/ty/subst.rs b/compiler/rustc_middle/src/ty/subst.rs
index 3a524d7b0f30..6a746c3631e7 100644
--- a/compiler/rustc_middle/src/ty/subst.rs
+++ b/compiler/rustc_middle/src/ty/subst.rs
@@ -525,6 +525,7 @@ struct SubstFolder<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
+    #[inline]
     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
         self.tcx
     }