diff --git a/compiler/rustc_middle/src/traits/mod.rs b/compiler/rustc_middle/src/traits/mod.rs
index 1ccd6fb56d9..bda229c1263 100644
--- a/compiler/rustc_middle/src/traits/mod.rs
+++ b/compiler/rustc_middle/src/traits/mod.rs
@@ -250,9 +250,6 @@ pub enum ObligationCauseCode<'tcx> {
     /// A tuple is WF only if its middle elements are `Sized`.
     TupleElem,
 
-    /// This is the trait reference from the given projection.
-    ProjectionWf(ty::AliasTy<'tcx>),
-
     /// Must satisfy all of the where-clause predicates of the
     /// given item.
     ItemObligation(DefId),
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index e260fcd5e75..4282f42a2b1 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -2621,9 +2621,6 @@ fn note_obligation_cause_code<T>(
             ObligationCauseCode::TupleElem => {
                 err.note("only the last element of a tuple may have a dynamically sized type");
             }
-            ObligationCauseCode::ProjectionWf(data) => {
-                err.note(format!("required so that the projection `{data}` is well-formed"));
-            }
             ObligationCauseCode::ReferenceOutlivesReferent(ref_ty) => {
                 err.note(format!(
                     "required so that reference `{ref_ty}` does not outlive its referent"