diff --git a/libcxxabi/src/demangle/ItaniumDemangle.h b/libcxxabi/src/demangle/ItaniumDemangle.h
index 4dca309e3cbc..a237cf724df0 100644
--- a/libcxxabi/src/demangle/ItaniumDemangle.h
+++ b/libcxxabi/src/demangle/ItaniumDemangle.h
@@ -3576,7 +3576,11 @@ Node *AbstractManglingParser<Derived, Alloc>::parseType() {
     StringView Res = parseBareSourceName();
     if (Res.empty())
       return nullptr;
-    return make<NameType>(Res);
+    // Typically, <builtin-type>s are not considered substitution candidates,
+    // but the exception to that exception is vendor extended types (Itanium C++
+    // ABI 5.9.1).
+    Result = make<NameType>(Res);
+    break;
   }
   case 'D':
     switch (look(1)) {
diff --git a/libcxxabi/test/test_demangle.pass.cpp b/libcxxabi/test/test_demangle.pass.cpp
index bc99ca7cee9c..4e1c1f5d2340 100644
--- a/libcxxabi/test/test_demangle.pass.cpp
+++ b/libcxxabi/test/test_demangle.pass.cpp
@@ -29765,7 +29765,10 @@ const char* cases[][2] =
     {"____Z3foo_block_invoke.25", "invocation function for block in foo"},
     {"__Z1fv", "f()"},
 
-    {"_Z2tfIZUb_E1SEiv", "int tf<'block-literal'::S>()"}
+    {"_Z2tfIZUb_E1SEiv", "int tf<'block-literal'::S>()"},
+
+    // Vendor extension types are substitution candidates.
+    {"_Z1fu3fooS_", "f(foo, foo)"},
 };
 
 const unsigned N = sizeof(cases) / sizeof(cases[0]);
diff --git a/llvm/include/llvm/Demangle/ItaniumDemangle.h b/llvm/include/llvm/Demangle/ItaniumDemangle.h
index 4dca309e3cbc..a237cf724df0 100644
--- a/llvm/include/llvm/Demangle/ItaniumDemangle.h
+++ b/llvm/include/llvm/Demangle/ItaniumDemangle.h
@@ -3576,7 +3576,11 @@ Node *AbstractManglingParser<Derived, Alloc>::parseType() {
     StringView Res = parseBareSourceName();
     if (Res.empty())
       return nullptr;
-    return make<NameType>(Res);
+    // Typically, <builtin-type>s are not considered substitution candidates,
+    // but the exception to that exception is vendor extended types (Itanium C++
+    // ABI 5.9.1).
+    Result = make<NameType>(Res);
+    break;
   }
   case 'D':
     switch (look(1)) {