diff --git a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ExposedFields.java b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ExposedFields.java
index 848c5cccd4..98b5e6415d 100644
--- a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ExposedFields.java
+++ b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ExposedFields.java
@@ -29,6 +29,7 @@
  * Value object to capture the fields exposed by an {@link AggregationOperation}.
  * 
  * @author Oliver Gierke
+ * @author Thomas Darimont
  * @since 1.3
  */
 public class ExposedFields implements Iterable<ExposedField> {
@@ -151,13 +152,65 @@ public ExposedField getField(String name) {
 		return null;
 	}
 
+	/**
+	 * Returns whether the {@link ExposedFields} exposes no non-synthetic fields at all.
+	 * 
+	 * @return
+	 */
+	public boolean exposesNoNonSyntheticFields() {
+		return originalFields.isEmpty();
+	}
+
+	/**
+	 * Returns whether the {@link ExposedFields} exposes a single non-synthetic field only.
+	 * 
+	 * @return
+	 */
+	public boolean exposesSingleNonSyntheticFieldOnly() {
+		return originalFields.size() == 1;
+	}
+
+	/**
+	 * Returns whether the {@link ExposedFields} exposes no synthetic fields at all.
+	 * 
+	 * @return
+	 */
+	public boolean exposesNoSyntheticFields() {
+		return syntheticFields.isEmpty();
+	}
+
+	/**
+	 * Returns whether the {@link ExposedFields} exposes a single synthetic field only.
+	 * 
+	 * @return
+	 */
+	public boolean exposesSingleSytheticFieldOnly() {
+		return syntheticFields.size() == 1;
+	}
+
+	/**
+	 * Returns whether the {@link ExposedFields} exposes no fields at all.
+	 * 
+	 * @return
+	 */
+	public boolean exposesNoFields() {
+		return exposedFieldsCount() == 0;
+	}
+
 	/**
 	 * Returns whether the {@link ExposedFields} exposes a single field only.
 	 * 
 	 * @return
 	 */
 	public boolean exposesSingleFieldOnly() {
-		return originalFields.size() + syntheticFields.size() == 1;
+		return exposedFieldsCount() == 1;
+	}
+
+	/**
+	 * @return
+	 */
+	private int exposedFieldsCount() {
+		return originalFields.size() + syntheticFields.size();
 	}
 
 	/* 
diff --git a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/GroupOperation.java b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/GroupOperation.java
index e3d8f1f3a6..7cf3c573f1 100644
--- a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/GroupOperation.java
+++ b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/GroupOperation.java
@@ -40,7 +40,11 @@
  */
 public class GroupOperation extends ExposedFieldsAggregationOperationContext implements AggregationOperation {
 
-	private final ExposedFields nonSynthecticFields;
+	/**
+	 * Holds the non-synthetic fields which are the fields of the group-id structure.
+	 */
+	private final ExposedFields idFields;
+
 	private final List<Operation> operations;
 
 	/**
@@ -50,7 +54,7 @@ public class GroupOperation extends ExposedFieldsAggregationOperationContext imp
 	 */
 	public GroupOperation(Fields fields) {
 
-		this.nonSynthecticFields = ExposedFields.nonSynthetic(fields);
+		this.idFields = ExposedFields.nonSynthetic(fields);
 		this.operations = new ArrayList<Operation>();
 	}
 
@@ -74,7 +78,7 @@ private GroupOperation(GroupOperation groupOperation, List<Operation> nextOperat
 		Assert.notNull(groupOperation, "GroupOperation must not be null!");
 		Assert.notNull(nextOperations, "NextOperations must not be null!");
 
-		this.nonSynthecticFields = groupOperation.nonSynthecticFields;
+		this.idFields = groupOperation.idFields;
 		this.operations = new ArrayList<Operation>(nextOperations.size() + 1);
 		this.operations.addAll(groupOperation.operations);
 		this.operations.addAll(nextOperations);
@@ -261,7 +265,7 @@ private GroupOperationBuilder newBuilder(Keyword keyword, String reference, Obje
 	@Override
 	public ExposedFields getFields() {
 
-		ExposedFields fields = this.nonSynthecticFields.and(new ExposedField(Fields.UNDERSCORE_ID, true));
+		ExposedFields fields = this.idFields.and(new ExposedField(Fields.UNDERSCORE_ID, true));
 
 		for (Operation operation : operations) {
 			fields = fields.and(operation.asField());
@@ -279,16 +283,20 @@ public com.mongodb.DBObject toDBObject(AggregationOperationContext context) {
 
 		BasicDBObject operationObject = new BasicDBObject();
 
-		if (nonSynthecticFields.exposesSingleFieldOnly()) {
+		if (idFields.exposesNoNonSyntheticFields()) {
+
+			operationObject.put(Fields.UNDERSCORE_ID, null);
+
+		} else if (idFields.exposesSingleNonSyntheticFieldOnly()) {
 
-			FieldReference reference = context.getReference(nonSynthecticFields.iterator().next());
+			FieldReference reference = context.getReference(idFields.iterator().next());
 			operationObject.put(Fields.UNDERSCORE_ID, reference.toString());
 
 		} else {
 
 			BasicDBObject inner = new BasicDBObject();
 
-			for (ExposedField field : nonSynthecticFields) {
+			for (ExposedField field : idFields) {
 				FieldReference reference = context.getReference(field);
 				inner.put(field.getName(), reference.toString());
 			}
diff --git a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/GroupOperationUnitTests.java b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/GroupOperationUnitTests.java
index b6d6484184..d5f71cc3a6 100644
--- a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/GroupOperationUnitTests.java
+++ b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/GroupOperationUnitTests.java
@@ -37,6 +37,38 @@ public void rejectsNullFields() {
 		new GroupOperation((Fields) null);
 	}
 
+	/**
+	 * @see DATAMONGO-759
+	 */
+	@Test
+	public void groupOperationWithNoGroupIdFieldsShouldGenerateNullAsGroupId() {
+
+		GroupOperation operation = new GroupOperation(Fields.from());
+		ExposedFields fields = operation.getFields();
+		DBObject groupClause = extractDbObjectFromGroupOperation(operation);
+
+		assertThat(fields.exposesSingleFieldOnly(), is(true));
+		assertThat(fields.exposesNoFields(), is(false));
+		assertThat(groupClause.get(UNDERSCORE_ID), is(nullValue()));
+	}
+
+	/**
+	 * @see DATAMONGO-759
+	 */
+	@Test
+	public void groupOperationWithNoGroupIdFieldsButAdditionalFieldsShouldGenerateNullAsGroupId() {
+
+		GroupOperation operation = new GroupOperation(Fields.from()).count().as("cnt").last("foo").as("foo");
+		ExposedFields fields = operation.getFields();
+		DBObject groupClause = extractDbObjectFromGroupOperation(operation);
+
+		assertThat(fields.exposesSingleFieldOnly(), is(false));
+		assertThat(fields.exposesNoFields(), is(false));
+		assertThat(groupClause.get(UNDERSCORE_ID), is(nullValue()));
+		assertThat((BasicDBObject) groupClause.get("cnt"), is(new BasicDBObject("$sum", 1)));
+		assertThat((BasicDBObject) groupClause.get("foo"), is(new BasicDBObject("$last", "$foo")));
+	}
+
 	@Test
 	public void createsGroupOperationWithSingleField() {