Index: libcxxabi/src/demangle/ItaniumDemangle.h
===================================================================
--- libcxxabi/src/demangle/ItaniumDemangle.h
+++ libcxxabi/src/demangle/ItaniumDemangle.h
@@ -3108,15 +3108,6 @@
 
   Node *SoFar = nullptr;
   while (!consumeIf('E')) {
-    consumeIf('L'); // extension
-
-    if (consumeIf('M')) {
-      // <data-member-prefix> := <member source-name> [<template-args>] M
-      if (SoFar == nullptr)
-        return nullptr;
-      continue;
-    }
-
     if (State)
       // Only set end-with-template on the case that does that.
       State->EndsWithTemplateArgs = false;
@@ -3161,12 +3152,17 @@
         return nullptr;
       continue; // Do not push a new substitution.
     } else {
+      consumeIf('L'); // extension
       //          ::= [<prefix>] <unqualified-name>
       SoFar = getDerived().parseUnqualifiedName(State, SoFar);
     }
     if (SoFar == nullptr)
       return nullptr;
     Subs.push_back(SoFar);
+
+    // No longer used.
+    // <data-member-prefix> := <member source-name> [<template-args>] M
+    consumeIf('M');
   }
 
   if (SoFar == nullptr || Subs.empty())
Index: libcxxabi/test/test_demangle.pass.cpp
===================================================================
--- libcxxabi/test/test_demangle.pass.cpp
+++ libcxxabi/test/test_demangle.pass.cpp
@@ -29946,6 +29946,9 @@
     "_ZN3CLSIiEIiEE",
     "_ZN3CLSDtLi0EEE",
     "_ZN3CLSIiEEvNS_T_Ev",
+
+    "_ZN1fIiEEvNTUt_E",
+    "_ZNDTUt_Ev",
 };
 
 const unsigned NI = sizeof(invalid_cases) / sizeof(invalid_cases[0]);
Index: llvm/include/llvm/Demangle/ItaniumDemangle.h
===================================================================
--- llvm/include/llvm/Demangle/ItaniumDemangle.h
+++ llvm/include/llvm/Demangle/ItaniumDemangle.h
@@ -3108,15 +3108,6 @@
 
   Node *SoFar = nullptr;
   while (!consumeIf('E')) {
-    consumeIf('L'); // extension
-
-    if (consumeIf('M')) {
-      // <data-member-prefix> := <member source-name> [<template-args>] M
-      if (SoFar == nullptr)
-        return nullptr;
-      continue;
-    }
-
     if (State)
       // Only set end-with-template on the case that does that.
       State->EndsWithTemplateArgs = false;
@@ -3161,12 +3152,17 @@
         return nullptr;
       continue; // Do not push a new substitution.
     } else {
+      consumeIf('L'); // extension
       //          ::= [<prefix>] <unqualified-name>
       SoFar = getDerived().parseUnqualifiedName(State, SoFar);
     }
     if (SoFar == nullptr)
       return nullptr;
     Subs.push_back(SoFar);
+
+    // No longer used.
+    // <data-member-prefix> := <member source-name> [<template-args>] M
+    consumeIf('M');
   }
 
   if (SoFar == nullptr || Subs.empty())