diff --git a/crates/hir-ty/src/display.rs b/crates/hir-ty/src/display.rs
index b3760e3a38..f0e31ebd02 100644
--- a/crates/hir-ty/src/display.rs
+++ b/crates/hir-ty/src/display.rs
@@ -620,19 +620,19 @@ impl HirDisplay for ProjectionTy {
                         .generic_predicates(id.parent)
                         .iter()
                         .map(|pred| pred.clone().substitute(Interner, &substs))
-                        .filter(|wc| match wc.skip_binders() {
-                            WhereClause::Implemented(tr) => {
-                                matches!(
-                                    tr.self_type_parameter(Interner).kind(Interner),
-                                    TyKind::Alias(_)
-                                )
-                            }
-                            WhereClause::TypeOutlives(t) => {
-                                matches!(t.ty.kind(Interner), TyKind::Alias(_))
-                            }
-                            // We shouldn't be here if these exist
-                            WhereClause::AliasEq(_) => false,
-                            WhereClause::LifetimeOutlives(_) => false,
+                        .filter(|wc| {
+                            let ty = match wc.skip_binders() {
+                                WhereClause::Implemented(tr) => tr.self_type_parameter(Interner),
+                                WhereClause::TypeOutlives(t) => t.ty.clone(),
+                                // We shouldn't be here if these exist
+                                WhereClause::AliasEq(_) | WhereClause::LifetimeOutlives(_) => {
+                                    return false;
+                                }
+                            };
+                            let TyKind::Alias(AliasTy::Projection(proj)) = ty.kind(Interner) else {
+                                return false;
+                            };
+                            proj == self
                         })
                         .collect::<Vec<_>>();
                     if !bounds.is_empty() {
diff --git a/crates/ide/src/inlay_hints.rs b/crates/ide/src/inlay_hints.rs
index 19e5509681..671fddb436 100644
--- a/crates/ide/src/inlay_hints.rs
+++ b/crates/ide/src/inlay_hints.rs
@@ -1065,4 +1065,34 @@ fn bar() {
 "#,
         );
     }
+
+    #[test]
+    fn regression_20239() {
+        check_with_config(
+            InlayHintsConfig { parameter_hints: true, type_hints: true, ..DISABLED_CONFIG },
+            r#"
+//- minicore: fn
+trait Iterator {
+    type Item;
+    fn map<B, F: FnMut(Self::Item) -> B>(self, f: F);
+}
+trait ToString {
+    fn to_string(&self);
+}
+
+fn check_tostr_eq<L, R>(left: L, right: R)
+where
+    L: Iterator,
+    L::Item: ToString,
+    R: Iterator,
+    R::Item: ToString,
+{
+    left.map(|s| s.to_string());
+           // ^ impl ToString
+    right.map(|s| s.to_string());
+            // ^ impl ToString
+}
+        "#,
+        );
+    }
 }