diff --git a/bson-kotlin/src/test/kotlin/org/bson/codecs/kotlin/DataClassCodecTest.kt b/bson-kotlin/src/test/kotlin/org/bson/codecs/kotlin/DataClassCodecTest.kt
index 40abc3a9cfa..e3cfe530705 100644
--- a/bson-kotlin/src/test/kotlin/org/bson/codecs/kotlin/DataClassCodecTest.kt
+++ b/bson-kotlin/src/test/kotlin/org/bson/codecs/kotlin/DataClassCodecTest.kt
@@ -25,6 +25,7 @@ import org.bson.codecs.configuration.CodecConfigurationException
 import org.bson.codecs.configuration.CodecRegistries.fromProviders
 import org.bson.codecs.kotlin.samples.Box
 import org.bson.codecs.kotlin.samples.DataClassEmbedded
+import org.bson.codecs.kotlin.samples.DataClassLastItemDefaultsToNull
 import org.bson.codecs.kotlin.samples.DataClassListOfDataClasses
 import org.bson.codecs.kotlin.samples.DataClassListOfListOfDataClasses
 import org.bson.codecs.kotlin.samples.DataClassListOfSealed
@@ -51,6 +52,7 @@ import org.bson.codecs.kotlin.samples.DataClassWithEnum
 import org.bson.codecs.kotlin.samples.DataClassWithEnumMapKey
 import org.bson.codecs.kotlin.samples.DataClassWithFailingInit
 import org.bson.codecs.kotlin.samples.DataClassWithInvalidBsonRepresentation
+import org.bson.codecs.kotlin.samples.DataClassWithListThatLastItemDefaultsToNull
 import org.bson.codecs.kotlin.samples.DataClassWithMutableList
 import org.bson.codecs.kotlin.samples.DataClassWithMutableMap
 import org.bson.codecs.kotlin.samples.DataClassWithMutableSet
@@ -133,6 +135,20 @@ class DataClassCodecTest {
         assertDecodesTo(withStoredNulls, dataClass)
     }
 
+    @Test
+    fun testDataClassWithListThatLastItemDefaultsToNull() {
+        val expected =
+            """{
+            | "elements": [{"required": "required"}, {"required": "required"}],
+            |}"""
+                .trimMargin()
+
+        val dataClass =
+            DataClassWithListThatLastItemDefaultsToNull(
+                listOf(DataClassLastItemDefaultsToNull("required"), DataClassLastItemDefaultsToNull("required")))
+        assertRoundTrips(expected, dataClass)
+    }
+
     @Test
     fun testDataClassWithNullableGenericsNotNull() {
         val expected =
diff --git a/bson-kotlin/src/test/kotlin/org/bson/codecs/kotlin/samples/DataClasses.kt b/bson-kotlin/src/test/kotlin/org/bson/codecs/kotlin/samples/DataClasses.kt
index 5bc6e768ed8..aa2c8983b1d 100644
--- a/bson-kotlin/src/test/kotlin/org/bson/codecs/kotlin/samples/DataClasses.kt
+++ b/bson-kotlin/src/test/kotlin/org/bson/codecs/kotlin/samples/DataClasses.kt
@@ -57,6 +57,10 @@ data class DataClassWithDefaults(
 
 data class DataClassWithNulls(val boolean: Boolean?, val string: String?, val listSimple: List<String?>?)
 
+data class DataClassWithListThatLastItemDefaultsToNull(val elements: List<DataClassLastItemDefaultsToNull>)
+
+data class DataClassLastItemDefaultsToNull(val required: String, val optional: String? = null)
+
 data class DataClassSelfReferential(
     val name: String,
     val left: DataClassSelfReferential? = null,
diff --git a/bson-kotlinx/src/main/kotlin/org/bson/codecs/kotlinx/BsonEncoder.kt b/bson-kotlinx/src/main/kotlin/org/bson/codecs/kotlinx/BsonEncoder.kt
index b3ae0c8cdf4..75080254cdb 100644
--- a/bson-kotlinx/src/main/kotlin/org/bson/codecs/kotlinx/BsonEncoder.kt
+++ b/bson-kotlinx/src/main/kotlin/org/bson/codecs/kotlinx/BsonEncoder.kt
@@ -72,7 +72,7 @@ internal class DefaultBsonEncoder(
     private var isPolymorphic = false
     private var state = STATE.VALUE
     private var mapState = MapState()
-    private var deferredElementName: String? = null
+    private val deferredElementHandler: DeferredElementHandler = DeferredElementHandler()
 
     override fun shouldEncodeElementDefault(descriptor: SerialDescriptor, index: Int): Boolean =
         configuration.encodeDefaults
@@ -117,7 +117,7 @@ internal class DefaultBsonEncoder(
             is StructureKind.CLASS -> {
                 val elementName = descriptor.getElementName(index)
                 if (descriptor.getElementDescriptor(index).isNullable) {
-                    deferredElementName = elementName
+                    deferredElementHandler.set(elementName)
                 } else {
                     encodeName(elementName)
                 }
@@ -140,25 +140,27 @@ internal class DefaultBsonEncoder(
     }
 
     override fun <T> encodeSerializableValue(serializer: SerializationStrategy<T>, value: T) {
-        deferredElementName?.let {
-            if (value != null || configuration.explicitNulls) {
-                encodeName(it)
-                super.encodeSerializableValue(serializer, value)
-            } else {
-                deferredElementName = null
-            }
-        }
-            ?: super.encodeSerializableValue(serializer, value)
+        deferredElementHandler.with(
+            {
+                // When using generics its possible for `value` to be null
+                // See: https://youtrack.jetbrains.com/issue/KT-66206
+                if (value != null || configuration.explicitNulls) {
+                    encodeName(it)
+                    super.encodeSerializableValue(serializer, value)
+                }
+            },
+            { super.encodeSerializableValue(serializer, value) })
     }
 
     override fun <T : Any> encodeNullableSerializableValue(serializer: SerializationStrategy<T>, value: T?) {
-        deferredElementName?.let {
-            if (value != null || configuration.explicitNulls) {
-                encodeName(it)
-                super.encodeNullableSerializableValue(serializer, value)
-            }
-        }
-            ?: super.encodeNullableSerializableValue(serializer, value)
+        deferredElementHandler.with(
+            {
+                if (value != null || configuration.explicitNulls) {
+                    encodeName(it)
+                    super.encodeNullableSerializableValue(serializer, value)
+                }
+            },
+            { super.encodeNullableSerializableValue(serializer, value) })
     }
 
     override fun encodeByte(value: Byte) = encodeInt(value.toInt())
@@ -170,14 +172,7 @@ internal class DefaultBsonEncoder(
     override fun encodeDouble(value: Double) = writer.writeDouble(value)
     override fun encodeInt(value: Int) = writer.writeInt32(value)
     override fun encodeLong(value: Long) = writer.writeInt64(value)
-    override fun encodeNull() {
-        deferredElementName?.let {
-            if (configuration.explicitNulls) {
-                encodeName(it)
-            }
-        }
-        writer.writeNull()
-    }
+    override fun encodeNull() = writer.writeNull()
 
     override fun encodeString(value: String) {
         when (state) {
@@ -206,7 +201,6 @@ internal class DefaultBsonEncoder(
 
     private fun encodeName(value: Any) {
         writer.writeName(value.toString())
-        deferredElementName = null
         state = STATE.VALUE
     }
 
@@ -229,4 +223,25 @@ internal class DefaultBsonEncoder(
             return getState()
         }
     }
+
+    private class DeferredElementHandler {
+        private var deferredElementName: String? = null
+
+        fun set(name: String) {
+            assert(deferredElementName == null) { -> "Overwriting an existing deferred name" }
+            deferredElementName = name
+        }
+
+        fun with(actionWithDeferredElement: (String) -> Unit, actionWithoutDeferredElement: () -> Unit): Unit {
+            deferredElementName?.let {
+                reset()
+                actionWithDeferredElement(it)
+            }
+                ?: actionWithoutDeferredElement()
+        }
+
+        private fun reset() {
+            deferredElementName = null
+        }
+    }
 }
diff --git a/bson-kotlinx/src/test/kotlin/org/bson/codecs/kotlinx/KotlinSerializerCodecTest.kt b/bson-kotlinx/src/test/kotlin/org/bson/codecs/kotlinx/KotlinSerializerCodecTest.kt
index ed9e1bfb43a..05a0d3ffd7d 100644
--- a/bson-kotlinx/src/test/kotlin/org/bson/codecs/kotlinx/KotlinSerializerCodecTest.kt
+++ b/bson-kotlinx/src/test/kotlin/org/bson/codecs/kotlinx/KotlinSerializerCodecTest.kt
@@ -45,6 +45,7 @@ import org.bson.codecs.kotlinx.samples.DataClassContainsOpen
 import org.bson.codecs.kotlinx.samples.DataClassContainsValueClass
 import org.bson.codecs.kotlinx.samples.DataClassEmbedded
 import org.bson.codecs.kotlinx.samples.DataClassKey
+import org.bson.codecs.kotlinx.samples.DataClassLastItemDefaultsToNull
 import org.bson.codecs.kotlinx.samples.DataClassListOfDataClasses
 import org.bson.codecs.kotlinx.samples.DataClassListOfListOfDataClasses
 import org.bson.codecs.kotlinx.samples.DataClassListOfSealed
@@ -78,6 +79,7 @@ import org.bson.codecs.kotlinx.samples.DataClassWithEncodeDefault
 import org.bson.codecs.kotlinx.samples.DataClassWithEnum
 import org.bson.codecs.kotlinx.samples.DataClassWithEnumMapKey
 import org.bson.codecs.kotlinx.samples.DataClassWithFailingInit
+import org.bson.codecs.kotlinx.samples.DataClassWithListThatLastItemDefaultsToNull
 import org.bson.codecs.kotlinx.samples.DataClassWithMutableList
 import org.bson.codecs.kotlinx.samples.DataClassWithMutableMap
 import org.bson.codecs.kotlinx.samples.DataClassWithMutableSet
@@ -255,6 +257,27 @@ class KotlinSerializerCodecTest {
         assertRoundTrips(expectedNulls, dataClass, altConfiguration)
     }
 
+    @Test
+    fun testDataClassWithListThatLastItemDefaultsToNull() {
+        val expectedWithOutNulls =
+            """{
+            | "elements": [{"required": "required"}, {"required": "required"}],
+            |}"""
+                .trimMargin()
+
+        val dataClass =
+            DataClassWithListThatLastItemDefaultsToNull(
+                listOf(DataClassLastItemDefaultsToNull("required"), DataClassLastItemDefaultsToNull("required")))
+        assertRoundTrips(expectedWithOutNulls, dataClass)
+
+        val expectedWithNulls =
+            """{
+            | "elements": [{"required": "required", "optional": null}, {"required": "required", "optional": null}],
+            |}"""
+                .trimMargin()
+        assertRoundTrips(expectedWithNulls, dataClass, BsonConfiguration(explicitNulls = true))
+    }
+
     @Test
     fun testDataClassWithNullableGenericsNotNull() {
         val expected =
diff --git a/bson-kotlinx/src/test/kotlin/org/bson/codecs/kotlinx/samples/DataClasses.kt b/bson-kotlinx/src/test/kotlin/org/bson/codecs/kotlinx/samples/DataClasses.kt
index 2511c7b0418..66907bff103 100644
--- a/bson-kotlinx/src/test/kotlin/org/bson/codecs/kotlinx/samples/DataClasses.kt
+++ b/bson-kotlinx/src/test/kotlin/org/bson/codecs/kotlinx/samples/DataClasses.kt
@@ -82,6 +82,11 @@ data class DataClassWithDefaults(
 
 @Serializable data class DataClassWithNulls(val boolean: Boolean?, val string: String?, val listSimple: List<String?>?)
 
+@Serializable
+data class DataClassWithListThatLastItemDefaultsToNull(val elements: List<DataClassLastItemDefaultsToNull>)
+
+@Serializable data class DataClassLastItemDefaultsToNull(val required: String, val optional: String? = null)
+
 @Serializable
 data class DataClassSelfReferential(
     val name: String,