Index: cfe/trunk/lib/AST/MicrosoftMangle.cpp
===================================================================
--- cfe/trunk/lib/AST/MicrosoftMangle.cpp
+++ cfe/trunk/lib/AST/MicrosoftMangle.cpp
@@ -884,11 +884,13 @@
         // associate typedef mangled in if they have one.
         Name += "<unnamed-type-";
         Name += TND->getName();
-      } else if (auto *ED = dyn_cast<EnumDecl>(TD)) {
-        auto EnumeratorI = ED->enumerator_begin();
-        assert(EnumeratorI != ED->enumerator_end());
+      } else if (isa<EnumDecl>(TD) &&
+                 cast<EnumDecl>(TD)->enumerator_begin() !=
+                     cast<EnumDecl>(TD)->enumerator_end()) {
+        // Anonymous non-empty enums mangle in the first enumerator.
+        auto *ED = cast<EnumDecl>(TD);
         Name += "<unnamed-enum-";
-        Name += EnumeratorI->getName();
+        Name += ED->enumerator_begin()->getName();
       } else {
         // Otherwise, number the types using a $S prefix.
         Name += "<unnamed-type-$S";
Index: cfe/trunk/test/CodeGenCXX/mangle-ms-cxx11.cpp
===================================================================
--- cfe/trunk/test/CodeGenCXX/mangle-ms-cxx11.cpp
+++ cfe/trunk/test/CodeGenCXX/mangle-ms-cxx11.cpp
@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -std=c++11 -fms-extensions -emit-llvm %s -o - -triple=i386-pc-win32 -fms-compatibility-version=19.00 | FileCheck %s --check-prefix=CHECK --check-prefix=MSVC2015
 // RUN: %clang_cc1 -std=c++11 -fms-extensions -emit-llvm %s -o - -triple=i386-pc-win32 -fms-compatibility-version=18.00 | FileCheck %s --check-prefix=CHECK --check-prefix=MSVC2013
+// RUN: %clang_cc1 -std=c++11 -fms-extensions -emit-llvm %s -o - -triple=i386-pc-win32 -gcodeview -debug-info-kind=limited | FileCheck %s --check-prefix=DBG
 
 namespace FTypeWithQuals {
 template <typename T>
@@ -350,3 +351,10 @@
 void f(decltype(enumerator)) {}
 // CHECK-DAG: define internal void @"?f@@YAXW4<unnamed-enum-enumerator>@@@Z"(
 void use_f() { f(enumerator); }
+
+namespace pr37723 {
+struct s { enum {}; enum {}; };
+// DBG-DAG: DW_TAG_enumeration_type{{.*}}identifier: ".?AW4<unnamed-type-$S2>@s@pr37723@@"
+// DBG-DAG: DW_TAG_enumeration_type{{.*}}identifier: ".?AW4<unnamed-type-$S3>@s@pr37723@@"
+s x;
+}