Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -356,6 +356,9 @@
   `Issue 51227 <https://github.com/llvm/llvm-project/issues/51227>`_.
 - Fix the bug of inserting the ``ZeroInitializationFixit`` before the template
   argument list of ``VarTemplateSpecializationDecl``.
+- Fix crash on invalid code when looking up a destructor in a templated class
+  inside a namespace. This fixes
+  `Issue 59446 <https://github.com/llvm/llvm-project/issues/59446>`_.
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Index: clang/lib/Sema/SemaExprCXX.cpp
===================================================================
--- clang/lib/Sema/SemaExprCXX.cpp
+++ clang/lib/Sema/SemaExprCXX.cpp
@@ -391,7 +391,7 @@
     //
     // also looks for type-name in the scope. Unfortunately, we can't
     // reasonably apply this fallback for dependent nested-name-specifiers.
-    if (SS.getScopeRep()->getPrefix()) {
+    if (SS.isValid() && SS.getScopeRep()->getPrefix()) {
       if (ParsedType T = LookupInScope()) {
         Diag(SS.getEndLoc(), diag::ext_qualified_dtor_named_in_lexical_scope)
             << FixItHint::CreateRemoval(SS.getRange());
Index: clang/test/SemaCXX/GH59446.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/GH59446.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
+
+namespace GH59446 { // expected-note {{to match this '{'}}
+namespace N {
+    template <typename T> struct X ; // expected-note 2 {{template is declared here}}
+                                     // expected-note@-1 {{'N::X' declared here}}
+				     // expected-note@-2 {{non-type declaration found by destructor name lookup}}
+  }
+  void f(X<int> *x) { // expected-error {{no template named 'X'; did you mean 'N::X'}}
+    x->N::X<int>::~X(); // expected-error 2 {{implicit instantiation of undefined template 'GH59446::N::X<int>'}}
+                        // expected-error@-1 {{identifier 'X' after '~' in destructor name does not name a type}}
+} // expected-error {{expected '}'}}