2 files changed, 16 insertions, 4 deletions
diff --git a/src/google/protobuf/compiler/csharp/csharp_enum.cc b/src/google/protobuf/compiler/csharp/csharp_enum.cc
index 9e4da1ed..9759e3ef 100644
--- a/src/google/protobuf/compiler/csharp/csharp_enum.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_enum.cc
@@ -65,6 +65,7 @@ void EnumGenerator::Generate(io::Printer* printer) {
                  "name", descriptor_->name());
   printer->Indent();
   std::set<string> used_names;
+  std::set<int> used_number;
   for (int i = 0; i < descriptor_->value_count(); i++) {
       WriteEnumValueDocComment(printer, descriptor_->value(i));
       string original_name = descriptor_->value(i)->name();
@@ -76,10 +77,18 @@ void EnumGenerator::Generate(io::Printer* printer) {
           << ") in " << descriptor_->name() << "; adding underscore to distinguish";
         name += "_";
       }
-      printer->Print("[pbr::OriginalName(\"$original_name$\")] $name$ = $number$,\n",
-         "original_name", original_name,
-         "name", name,
-         "number", SimpleItoa(descriptor_->value(i)->number()));         
+      int number = descriptor_->value(i)->number();
+      if (!used_number.insert(number).second) {
+          printer->Print("[pbr::OriginalName(\"$original_name$\", PreferredAlias = false)] $name$ = $number$,\n",
+             "original_name", original_name,
+             "name", name,
+             "number", SimpleItoa(number));
+      } else {
+          printer->Print("[pbr::OriginalName(\"$original_name$\")] $name$ = $number$,\n",
+             "original_name", original_name,
+             "name", name,
+             "number", SimpleItoa(number));
+      }
   }
   printer->Outdent();
   printer->Print("}\n");
diff --git a/src/google/protobuf/unittest_proto3.proto b/src/google/protobuf/unittest_proto3.proto
index f59d2178..a27b1b26 100644
--- a/src/google/protobuf/unittest_proto3.proto
+++ b/src/google/protobuf/unittest_proto3.proto
@@ -200,6 +200,9 @@ message TestMutualRecursionB {
   int32 optional_int32 = 2;
 }
 
+message TestEnumAllowAlias {
+  TestEnumWithDupValue value = 1;
+}
 
 // Test an enum that has multiple values with the same number.
 enum TestEnumWithDupValue {