diff --git a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/query/PartTreeMongoQuery.java b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/query/PartTreeMongoQuery.java
index 606d865e0..2dbe49b7d 100644
--- a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/query/PartTreeMongoQuery.java
+++ b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/query/PartTreeMongoQuery.java
@@ -100,7 +100,7 @@ public class PartTreeMongoQuery extends AbstractMongoQuery {
 
 			ReturnedType returnedType = processor.withDynamicProjection(accessor).getReturnedType();
 
-			if (returnedType.isProjecting()) {
+			if (returnedType.needsCustomConstruction()) {
 
 				Field fields = query.fields();
 
diff --git a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/query/PartTreeMongoQueryUnitTests.java b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/query/PartTreeMongoQueryUnitTests.java
index 21cfa5c13..341ea8880 100644
--- a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/query/PartTreeMongoQueryUnitTests.java
+++ b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/query/PartTreeMongoQueryUnitTests.java
@@ -31,6 +31,7 @@ import org.junit.rules.ExpectedException;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
 import org.mockito.junit.MockitoJUnitRunner;
+import org.springframework.beans.factory.annotation.Value;
 import org.springframework.data.mongodb.MongoDbFactory;
 import org.springframework.data.mongodb.core.MongoOperations;
 import org.springframework.data.mongodb.core.convert.DbRefResolver;
@@ -172,6 +173,14 @@ public class PartTreeMongoQueryUnitTests {
 		assertThat(query.getFieldsObject().get("firstname"), is((Object) 1));
 	}
 
+	@Test // DATAMONGO-1729
+	public void doesNotCreateFieldsObjectForOpenProjection() {
+
+		org.springframework.data.mongodb.core.query.Query query = deriveQueryFromMethod("findAllBy");
+
+		assertThat(query.getFieldsObject(), is(nullValue()));
+	}
+
 	private org.springframework.data.mongodb.core.query.Query deriveQueryFromMethod(String method, Object... args) {
 
 		Class<?>[] types = new Class<?>[args.length];
@@ -232,6 +241,8 @@ public class PartTreeMongoQueryUnitTests {
 
 		@Query(fields = "{ 'firstname' : 1 }")
 		List<Person> findBySex(Sex sex);
+
+		OpenProjection findAllBy();
 	}
 
 	interface PersonProjection {
@@ -256,4 +267,12 @@ public class PartTreeMongoQueryUnitTests {
 			this.lastname = lastname;
 		}
 	}
+
+	interface OpenProjection {
+
+		String getFirstname();
+
+		@Value("#{target.firstname + ' ' + target.lastname}")
+		String getFullname();
+	}
 }