1 files changed, 12 insertions, 0 deletions
diff --git a/csharp/src/Google.Protobuf/Reflection/PartialClasses.cs b/csharp/src/Google.Protobuf/Reflection/PartialClasses.cs
index c7ed4342..8c055d6d 100644
--- a/csharp/src/Google.Protobuf/Reflection/PartialClasses.cs
+++ b/csharp/src/Google.Protobuf/Reflection/PartialClasses.cs
@@ -44,4 +44,16 @@ namespace Google.Protobuf.Reflection
             OneofIndex = -1;
         }
     }
+
+    internal partial class FieldOptions
+    {
+        // We can't tell the difference between "explicitly set to false" and "not set"
+        // in proto3, but we need to tell the difference for FieldDescriptor.IsPacked.
+        // This won't work if we ever need to support proto2, but at that point we'll be
+        // able to remove this hack and use field presence instead. 
+        partial void OnConstruction()
+        {
+            Packed = true;
+        }
+    }
 }
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