diff --git a/csharp/src/Google.Protobuf/FieldCodec.cs b/csharp/src/Google.Protobuf/FieldCodec.cs
index 9831308..a11f242 100644
--- a/csharp/src/Google.Protobuf/FieldCodec.cs
+++ b/csharp/src/Google.Protobuf/FieldCodec.cs
@@ -30,6 +30,7 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #endregion
 
+using Google.Protobuf.Collections;
 using Google.Protobuf.Compatibility;
 using Google.Protobuf.WellKnownTypes;
 using System;
@@ -346,8 +347,10 @@
     /// </remarks>
     public sealed class FieldCodec<T>
     {
+        private static readonly EqualityComparer<T> EqualityComparer = ProtobufEqualityComparers.GetEqualityComparer<T>();
         private static readonly T DefaultDefault;
-        private static readonly bool TypeSupportsPacking = typeof(T).IsValueType() && Nullable.GetUnderlyingType(typeof(T)) == null;
+        // Only non-nullable value types support packing. This is the simplest way of detecting that.
+        private static readonly bool TypeSupportsPacking = default(T) != null;
 
         static FieldCodec()
         {
@@ -468,6 +471,6 @@
         /// </summary>
         public int CalculateSizeWithTag(T value) => IsDefault(value) ? 0 : ValueSizeCalculator(value) + tagSize;
 
-        private bool IsDefault(T value) => EqualityComparer<T>.Default.Equals(value, DefaultValue);
+        private bool IsDefault(T value) => EqualityComparer.Equals(value, DefaultValue);
     }
 }