diff --git a/gcc/rust/typecheck/rust-tyty-util.cc b/gcc/rust/typecheck/rust-tyty-util.cc
index c6c740b2cba..72761d9842b 100644
--- a/gcc/rust/typecheck/rust-tyty-util.cc
+++ b/gcc/rust/typecheck/rust-tyty-util.cc
@@ -30,7 +30,8 @@ TyVar::TyVar (HirId ref) : ref (ref)
   auto context = Resolver::TypeCheckContext::get ();
   BaseType *lookup = nullptr;
   bool ok = context->lookup_type (ref, &lookup);
-  rust_assert (ok);
+  if (!ok || lookup == nullptr || lookup->get_kind () == TypeKind::ERROR)
+    return;
 }
 
 BaseType *
@@ -39,7 +40,8 @@ TyVar::get_tyty () const
   auto context = Resolver::TypeCheckContext::get ();
   BaseType *lookup = nullptr;
   bool ok = context->lookup_type (ref, &lookup);
-  rust_assert (ok);
+  if (!ok || lookup == nullptr)
+    return nullptr;
   return lookup;
 }
 
@@ -95,7 +97,10 @@ TyVar::subst_covariant_var (TyTy::BaseType *orig, TyTy::BaseType *subst)
 TyVar
 TyVar::clone () const
 {
-  TyTy::BaseType *c = get_tyty ()->clone ();
+  TyTy::BaseType *base = get_tyty ();
+  if (base == nullptr || base->get_kind () == TypeKind::ERROR)
+    return TyVar::get_implicit_infer_var (UNKNOWN_LOCATION);
+  TyTy::BaseType *c = base->clone ();
   return TyVar (c->get_ref ());
 }
 
@@ -105,6 +110,10 @@ TyVar::monomorphized_clone () const
   auto &mappings = Analysis::Mappings::get ();
   auto context = Resolver::TypeCheckContext::get ();
 
+  TyTy::BaseType *base = get_tyty ();
+  if (base == nullptr || base->get_kind () == TypeKind::ERROR)
+    return TyVar::get_implicit_infer_var (UNKNOWN_LOCATION);
+
   // this needs a new hirid
   TyTy::BaseType *c = get_tyty ()->monomorphized_clone ();
   c->set_ref (mappings.get_next_hir_id ());
diff --git a/gcc/testsuite/rust/compile/issue-3556.rs b/gcc/testsuite/rust/compile/issue-3556.rs
new file mode 100644
index 00000000000..be7d85a93b5
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-3556.rs
@@ -0,0 +1,4 @@
+fn main() {
+    let ref mut a @ (ref mut b,);
+    // { dg-error "expected T\\?, found tuple" "" { target *-*-* } .-1 }
+}
\ No newline at end of file