diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index 2a2b491bcbdf..66bccbe45845 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -1704,7 +1704,8 @@ void CXXNameMangler::mangleTemplateParamDecl(const NamedDecl *Decl) {
       QualType T = Tn->getType();
       if (Tn->isParameterPack()) {
         Out << "Tp";
-        T = T->castAs<PackExpansionType>()->getPattern();
+        if (auto *PackExpansion = T->getAs<PackExpansionType>())
+          T = PackExpansion->getPattern();
       }
       Out << "Tn";
       mangleType(T);
diff --git a/clang/test/CodeGenCXX/mangle-lambda-explicit-template-params.cpp b/clang/test/CodeGenCXX/mangle-lambda-explicit-template-params.cpp
index dba10fbf01db..45fdec30f988 100644
--- a/clang/test/CodeGenCXX/mangle-lambda-explicit-template-params.cpp
+++ b/clang/test/CodeGenCXX/mangle-lambda-explicit-template-params.cpp
@@ -54,6 +54,12 @@ inline void collision() {
 }
 void use_collision() { collision(); }
 
+namespace pack_not_pack_expansion {
+  template<typename T, int, T...> struct X;
+  // CHECK: @_ZNK23pack_not_pack_expansion1xMUlTyTtTyTnT_TpTnTL0__ETpTyvE_clIiNS_1XEJfEEEDav
+  inline auto x = []<typename T, template<typename U, T, U...> typename, typename ...V>(){}; void f() { x.operator()<int, X, float>(); }
+}
+
 template<typename> void f() {
   // CHECK: define linkonce_odr {{.*}} @_ZZ1fIiEvvENKUlT_E_clIiEEDaS0_(
   auto x = [](auto){};