diff --git a/src/Mandrill.net/Serialization/MandrillMergeVarConverter.cs b/src/Mandrill.net/Serialization/MandrillMergeVarConverter.cs
index 10c34f8..647e46a 100644
--- a/src/Mandrill.net/Serialization/MandrillMergeVarConverter.cs
+++ b/src/Mandrill.net/Serialization/MandrillMergeVarConverter.cs
@@ -33,9 +33,18 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
             writer.WriteStartObject();
             writer.WritePropertyName("name");
             writer.WriteValue(mergeVar.Name);
-            var content = JToken.FromObject((object)mergeVar.Content, _contentSerializer);
             writer.WritePropertyName("content");
-            content.WriteTo(writer);
+            var content = (object)mergeVar.Content;
+            if (content == null)
+            {
+                writer.WriteNull();
+            }
+            else
+            {
+                var token = JToken.FromObject(content, _contentSerializer);
+                token.WriteTo(writer);
+            }
+
             writer.WriteEndObject();
         }
     }
diff --git a/tests/SerializationTests.cs b/tests/SerializationTests.cs
index dad643f..4f20767 100644
--- a/tests/SerializationTests.cs
+++ b/tests/SerializationTests.cs
@@ -134,6 +134,27 @@ public void Can_serialize_merge_var_content_using_custom_settings()
             result["LastName"].Value<string>().Should().BeNull();
         }
 
+        [Fact]
+        public void Can_serialize_merge_var_with_null_content()
+        {
+            var message = new MandrillMessage();
+            string data = null;
+
+            message.GlobalMergeVars.Add(new MandrillMergeVar()
+            {
+                Name = "test",
+                Content = data
+            });
+
+            var json = JObject.FromObject(message, MandrillSerializer.Instance);
+
+            json["global_merge_vars"].Should().NotBeEmpty();
+            var result = json["global_merge_vars"].First["content"];
+
+            Output.WriteLine(json.ToString(Formatting.Indented));
+            result.ToObject<object>().Should().BeNull();
+        }
+
         [Fact]
         public void Can_set_property_name_by_convention()
         {