diff --git a/src/main/java/org/springframework/session/data/mongo/JacksonMongoSessionConverter.java b/src/main/java/org/springframework/session/data/mongo/JacksonMongoSessionConverter.java
index 38084f7..46e48d1 100644
--- a/src/main/java/org/springframework/session/data/mongo/JacksonMongoSessionConverter.java
+++ b/src/main/java/org/springframework/session/data/mongo/JacksonMongoSessionConverter.java
@@ -111,8 +111,10 @@ public class JacksonMongoSessionConverter extends AbstractMongoSessionConverter
 
 		try {
 			DBObject dbSession = (DBObject) JSON.parse(this.objectMapper.writeValueAsString(source));
-			dbSession.put(EXPIRE_AT_FIELD_NAME, source.getExpireAt());
+
+			// Override default serialization with proper values.
 			dbSession.put(PRINCIPAL_FIELD_NAME, extractPrincipal(source));
+			dbSession.put(EXPIRE_AT_FIELD_NAME, source.getExpireAt());
 			return dbSession;
 		} catch (JsonProcessingException e) {
 			throw new IllegalStateException("Cannot convert MongoExpiringSession", e);
@@ -123,8 +125,7 @@ public class JacksonMongoSessionConverter extends AbstractMongoSessionConverter
 	@Nullable
 	protected MongoSession convert(Document source) {
 
-		Date expireAt = source.getDate(EXPIRE_AT_FIELD_NAME);
-		source.remove(EXPIRE_AT_FIELD_NAME);
+		Date expireAt = (Date) source.remove(EXPIRE_AT_FIELD_NAME);
 		String json = source.toJson(JsonWriterSettings.builder().outputMode(JsonMode.RELAXED).build());
 
 		try {
diff --git a/src/test/java/org/springframework/session/data/mongo/JacksonMongoSessionConverterTest.java b/src/test/java/org/springframework/session/data/mongo/JacksonMongoSessionConverterTest.java
index 93fddba..12d8dff 100644
--- a/src/test/java/org/springframework/session/data/mongo/JacksonMongoSessionConverterTest.java
+++ b/src/test/java/org/springframework/session/data/mongo/JacksonMongoSessionConverterTest.java
@@ -44,7 +44,7 @@ public class JacksonMongoSessionConverterTest extends AbstractMongoSessionConver
 	}
 
 	@Test
-	public void shouldSaveIdField() throws Exception {
+	public void shouldSaveIdField() {
 
 		// given
 		MongoSession session = new MongoSession();
@@ -109,16 +109,19 @@ public class JacksonMongoSessionConverterTest extends AbstractMongoSessionConver
 
 		// given
 		Date now = new Date();
-		HashMap data = new HashMap();
+		HashMap<String, Object> data = new HashMap<>();
+
 		data.put("expireAt", now);
 		data.put("@class", MongoSession.class.getName());
 		data.put("_id", new ObjectId().toString());
+		
 		Document document = new Document(data);
 
 		// when
 		MongoSession convertedSession = this.mongoSessionConverter.convert(document);
 
 		// then
+		assertThat(convertedSession).isNotNull();
 		assertThat(convertedSession.getExpireAt()).isEqualTo(now);
 	}