diff --git a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/SpringDataMongodbSerializer.java b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/SpringDataMongodbSerializer.java
index 6fd82e837..d6881341b 100644
--- a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/SpringDataMongodbSerializer.java
+++ b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/SpringDataMongodbSerializer.java
@@ -126,15 +126,30 @@ class SpringDataMongodbSerializer extends MongodbSerializer {
 
 		value = value instanceof Optional ? ((Optional) value).orElse(null) : value;
 
-		if (ID_KEY.equals(key)) {
-			DBObject superIdValue = super.asDBObject(key, value);
-			Document mappedIdValue = mapper.getMappedObject((BasicDBObject) superIdValue, Optional.empty());
-			return (DBObject) JSON.parse(mappedIdValue.toJson());
+		if (key.endsWith(ID_KEY)) {
+			return convertId(key, value);
 		}
 
 		return super.asDBObject(key, value instanceof Pattern ? value : toQuerydslMongoType(value));
 	}
 
+	/**
+	 * Convert a given, already known to be an {@literal id} or even a nested document id, value into the according id
+	 * representation following the conversion rules of {@link QueryMapper#convertId(Object)}.
+	 *
+	 * @param key the property path to the given value.
+	 * @param idValue the raw {@literal id} value.
+	 * @return the {@literal id} representation in the required format.
+	 */
+	private DBObject convertId(String key, Object idValue) {
+
+		Object convertedId = mapper.convertId(idValue);
+
+		Document mappedIdValue = mapper.getMappedObject((BasicDBObject) super.asDBObject(key, convertedId),
+				Optional.empty());
+		return (DBObject) JSON.parse(mappedIdValue.toJson());
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see com.querydsl.mongodb.MongodbSerializer#isReference(com.querydsl.core.types.Path)
diff --git a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/support/QuerydslRepositorySupportTests.java b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/support/QuerydslRepositorySupportTests.java
index f4990bf9b..acaa18845 100644
--- a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/support/QuerydslRepositorySupportTests.java
+++ b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/support/QuerydslRepositorySupportTests.java
@@ -18,13 +18,18 @@ package org.springframework.data.mongodb.repository.support;
 import static org.hamcrest.CoreMatchers.*;
 import static org.junit.Assert.*;
 
+import lombok.Data;
+
 import java.util.Arrays;
 
+import org.bson.types.ObjectId;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.data.annotation.Id;
 import org.springframework.data.mongodb.core.MongoOperations;
+import org.springframework.data.mongodb.core.mapping.Document;
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.repository.Person;
 import org.springframework.data.mongodb.repository.QPerson;
@@ -49,7 +54,9 @@ public class QuerydslRepositorySupportTests {
 	@Before
 	public void setUp() {
 
+		operations.remove(new Query(), Outer.class);
 		operations.remove(new Query(), Person.class);
+
 		person = new Person("Dave", "Matthews");
 		operations.save(person);
 
@@ -97,4 +104,54 @@ public class QuerydslRepositorySupportTests {
 		assertThat(queryUsingIdField.fetchOne(), equalTo(person));
 		assertThat(queryUsingIdField.fetchOne(), equalTo(queryUsingRefObject.fetchOne()));
 	}
+
+	@Test // DATAMONGO-1998
+	public void shouldLeaveStringIdThatIsNoValidObjectIdAsItIs() {
+
+		Outer outer = new Outer();
+		outer.id = "outer-1";
+		outer.inner = new Inner();
+		outer.inner.id = "inner-1";
+		outer.inner.value = "go climb a rock";
+
+		operations.save(outer);
+
+		QQuerydslRepositorySupportTests_Outer o = QQuerydslRepositorySupportTests_Outer.outer;
+		SpringDataMongodbQuery<Outer> query = repoSupport.from(o).where(o.inner.id.eq(outer.inner.id));
+
+		assertThat(query.fetchOne(), equalTo(outer));
+	}
+
+	@Test // DATAMONGO-1998
+	public void shouldConvertStringIdThatIsAValidObjectIdIntoTheSuch() {
+
+		Outer outer = new Outer();
+		outer.id = new ObjectId().toHexString();
+		outer.inner = new Inner();
+		outer.inner.id = new ObjectId().toHexString();
+		outer.inner.value = "eat sleep workout repeat";
+
+		operations.save(outer);
+
+		QQuerydslRepositorySupportTests_Outer o = QQuerydslRepositorySupportTests_Outer.outer;
+		SpringDataMongodbQuery<Outer> query = repoSupport.from(o).where(o.inner.id.eq(outer.inner.id));
+
+		assertThat(query.fetchOne(), equalTo(outer));
+	}
+
+	@Data
+	@Document
+	public static class Outer {
+
+		@Id String id;
+		Inner inner;
+	}
+
+	@Data
+	public static class Inner {
+
+		@Id String id;
+		String value;
+
+	}
 }