diff --git a/compiler/rustc_middle/src/ty/assoc.rs b/compiler/rustc_middle/src/ty/assoc.rs
index 994936351ff..5cb2b90fe11 100644
--- a/compiler/rustc_middle/src/ty/assoc.rs
+++ b/compiler/rustc_middle/src/ty/assoc.rs
@@ -16,12 +16,10 @@ pub enum AssocItemContainer {
 }
 
 impl AssocItemContainer {
-    /// Asserts that this is the `DefId` of an associated item declared
-    /// in an impl, and returns the trait `DefId`.
-    pub fn assert_impl(&self) -> DefId {
+    pub fn impl_def_id(&self) -> Option<DefId> {
         match *self {
-            ImplContainer(id) => id,
-            _ => bug!("associated item has wrong container type: {:?}", self),
+            ImplContainer(id) => Some(id),
+            _ => None,
         }
     }
 
diff --git a/compiler/rustc_typeck/src/check/compare_method.rs b/compiler/rustc_typeck/src/check/compare_method.rs
index 0ce2746b128..a2ffb30f43b 100644
--- a/compiler/rustc_typeck/src/check/compare_method.rs
+++ b/compiler/rustc_typeck/src/check/compare_method.rs
@@ -1293,7 +1293,12 @@ pub fn check_type_bounds<'tcx>(
 
     tcx.infer_ctxt().enter(move |infcx| {
         // if the item is inside a const impl, we transform the predicates to be const.
-        let constness = tcx.impl_constness(impl_ty.container.assert_impl());
+        let constness = impl_ty
+            .container
+            .impl_def_id()
+            .map(|did| tcx.impl_constness(did))
+            .unwrap_or(hir::Constness::NotConst);
+
         let pred_map = match constness {
             hir::Constness::NotConst => |p, _| p,
             hir::Constness::Const => |p: ty::Predicate<'tcx>, tcx: TyCtxt<'tcx>| {