diff --git a/driver-async/src/main/com/mongodb/async/client/AggregateIterableImpl.java b/driver-async/src/main/com/mongodb/async/client/AggregateIterableImpl.java
index 59f140acee3..83c446337fc 100644
--- a/driver-async/src/main/com/mongodb/async/client/AggregateIterableImpl.java
+++ b/driver-async/src/main/com/mongodb/async/client/AggregateIterableImpl.java
@@ -186,13 +186,19 @@ private MongoNamespace getOutNamespace() {
         if (lastStageDocument.containsKey("$out")) {
             return new MongoNamespace(namespace.getDatabaseName(), lastStageDocument.getString("$out").getValue());
         } else if (lastStageDocument.containsKey("$merge")) {
-            BsonDocument mergeDocument = lastStageDocument.getDocument("$merge");
-            if (mergeDocument.isDocument("into")) {
-                BsonDocument intoDocument = mergeDocument.getDocument("into");
-                return new MongoNamespace(intoDocument.getString("db", new BsonString(namespace.getDatabaseName())).getValue(),
-                        intoDocument.getString("coll").getValue());
-            } else if (mergeDocument.isString("into")) {
-                return new MongoNamespace(namespace.getDatabaseName(), mergeDocument.getString("into").getValue());
+            if (lastStageDocument.isString("$merge")) {
+                return new MongoNamespace(namespace.getDatabaseName(), lastStageDocument.getString("$merge").getValue());
+            } else if (lastStageDocument.isDocument("$merge")) {
+                BsonDocument mergeDocument = lastStageDocument.getDocument("$merge");
+                if (mergeDocument.isDocument("into")) {
+                    BsonDocument intoDocument = mergeDocument.getDocument("into");
+                    return new MongoNamespace(intoDocument.getString("db", new BsonString(namespace.getDatabaseName())).getValue(),
+                            intoDocument.getString("coll").getValue());
+                } else if (mergeDocument.isString("into")) {
+                    return new MongoNamespace(namespace.getDatabaseName(), mergeDocument.getString("into").getValue());
+                }
+            } else {
+                throw new IllegalStateException("Cannot return a cursor when the value for $merge stage is not a string or a document");
             }
         }
 
diff --git a/driver-async/src/test/unit/com/mongodb/async/client/AggregateIterableSpecification.groovy b/driver-async/src/test/unit/com/mongodb/async/client/AggregateIterableSpecification.groovy
index 5e51916a453..deb99e1a3a2 100644
--- a/driver-async/src/test/unit/com/mongodb/async/client/AggregateIterableSpecification.groovy
+++ b/driver-async/src/test/unit/com/mongodb/async/client/AggregateIterableSpecification.groovy
@@ -209,7 +209,7 @@ class AggregateIterableSpecification extends Specification {
                 .comment('this is a comment'))
     }
 
-    def 'should build the expected AggregateToCollectionOperation for $merge'() {
+    def 'should build the expected AggregateToCollectionOperation for $merge document'() {
         given:
         def cursor = Stub(AsyncBatchCursor) {
             next(_) >> {
@@ -358,6 +358,38 @@ class AggregateIterableSpecification extends Specification {
                 .comment('this is a comment'))
     }
 
+    def 'should build the expected AggregateToCollectionOperation for $merge string'() {
+        given:
+        def cursor = Stub(AsyncBatchCursor) {
+            next(_) >> {
+                it[0].onResult(null, null)
+            }
+        }
+        def executor = new TestOperationExecutor([cursor, cursor, cursor, cursor, cursor, cursor, cursor]);
+        def collectionName = 'collectionName'
+        def collectionNamespace = new MongoNamespace(namespace.getDatabaseName(), collectionName)
+        def pipeline = [new Document('$match', 1), new Document('$merge', new Document('into', collectionName))]
+
+        when: 'aggregation includes $merge'
+        new AggregateIterableImpl(null, namespace, Document, Document, codecRegistry, readPreference, readConcern, writeConcern, executor,
+                pipeline, AggregationLevel.COLLECTION, true)
+                .into([]) { result, t -> }
+
+        def operation = executor.getReadOperation() as WriteOperationThenCursorReadOperation
+
+        then:
+        expect operation.getAggregateToCollectionOperation(), isTheSameAs(new AggregateToCollectionOperation(namespace,
+                [new BsonDocument('$match', new BsonInt32(1)),
+                 new BsonDocument('$merge', new BsonDocument('into', new BsonString(collectionName)))],
+                readConcern, writeConcern))
+
+        when:
+        operation = operation.getReadOperation() as FindOperation
+
+        then:
+        operation.getNamespace() == collectionNamespace
+    }
+
     def 'should handle exceptions correctly'() {
         given:
         def codecRegistry = fromProviders([new ValueCodecProvider(), new BsonValueCodecProvider()])
diff --git a/driver-sync/src/main/com/mongodb/client/internal/AggregateIterableImpl.java b/driver-sync/src/main/com/mongodb/client/internal/AggregateIterableImpl.java
index 56086cda801..629128eded8 100644
--- a/driver-sync/src/main/com/mongodb/client/internal/AggregateIterableImpl.java
+++ b/driver-sync/src/main/com/mongodb/client/internal/AggregateIterableImpl.java
@@ -187,13 +187,19 @@ private MongoNamespace getOutNamespace() {
         if (lastStageDocument.containsKey("$out")) {
             return new MongoNamespace(namespace.getDatabaseName(), lastStageDocument.getString("$out").getValue());
         } else if (lastStageDocument.containsKey("$merge")) {
-            BsonDocument mergeDocument = lastStageDocument.getDocument("$merge");
-            if (mergeDocument.isDocument("into")) {
-                BsonDocument intoDocument = mergeDocument.getDocument("into");
-                return new MongoNamespace(intoDocument.getString("db", new BsonString(namespace.getDatabaseName())).getValue(),
-                        intoDocument.getString("coll").getValue());
-            } else if (mergeDocument.isString("into")) {
-                return new MongoNamespace(namespace.getDatabaseName(), mergeDocument.getString("into").getValue());
+            if (lastStageDocument.isString("$merge")) {
+                return new MongoNamespace(namespace.getDatabaseName(), lastStageDocument.getString("$merge").getValue());
+            } else if (lastStageDocument.isDocument("$merge")) {
+                BsonDocument mergeDocument = lastStageDocument.getDocument("$merge");
+                if (mergeDocument.isDocument("into")) {
+                    BsonDocument intoDocument = mergeDocument.getDocument("into");
+                    return new MongoNamespace(intoDocument.getString("db", new BsonString(namespace.getDatabaseName())).getValue(),
+                            intoDocument.getString("coll").getValue());
+                } else if (mergeDocument.isString("into")) {
+                    return new MongoNamespace(namespace.getDatabaseName(), mergeDocument.getString("into").getValue());
+                }
+            } else {
+                throw new IllegalStateException("Cannot return a cursor when the value for $merge stage is not a string or a document");
             }
         }
 
diff --git a/driver-sync/src/test/unit/com/mongodb/client/internal/AggregateIterableSpecification.groovy b/driver-sync/src/test/unit/com/mongodb/client/internal/AggregateIterableSpecification.groovy
index d9d9adaa289..ca3030bfa7d 100644
--- a/driver-sync/src/test/unit/com/mongodb/client/internal/AggregateIterableSpecification.groovy
+++ b/driver-sync/src/test/unit/com/mongodb/client/internal/AggregateIterableSpecification.groovy
@@ -195,7 +195,7 @@ class AggregateIterableSpecification extends Specification {
                 .comment('this is a comment'))
     }
 
-    def 'should build the expected AggregateToCollectionOperation for $merge'() {
+    def 'should build the expected AggregateToCollectionOperation for $merge document'() {
         given:
         def executor = new TestOperationExecutor([null, null, null, null, null, null, null])
         def collectionName = 'collectionName'
@@ -335,6 +335,30 @@ class AggregateIterableSpecification extends Specification {
                 .comment('this is a comment'))
     }
 
+    def 'should build the expected AggregateToCollectionOperation for $merge string'() {
+        given:
+        def executor = new TestOperationExecutor([null, null, null, null, null, null, null])
+        def collectionName = 'collectionName'
+        def collectionNamespace = new MongoNamespace(namespace.getDatabaseName(), collectionName)
+        def pipeline = [new BsonDocument('$match', new BsonDocument()), new BsonDocument('$merge', new BsonString(collectionName))]
+
+        when:
+        new AggregateIterableImpl(null, namespace, Document, Document, codecRegistry, readPreference, readConcern, writeConcern, executor,
+                pipeline, AggregationLevel.COLLECTION, false)
+                .iterator()
+
+        def operation = executor.getWriteOperation() as AggregateToCollectionOperation
+
+        then:
+        expect operation, isTheSameAs(new AggregateToCollectionOperation(namespace, pipeline, readConcern, writeConcern,
+                AggregationLevel.COLLECTION))
+
+        when:
+        operation = executor.getReadOperation() as FindOperation<Document>
+
+        then:
+        operation.getNamespace() == collectionNamespace
+    }
 
     def 'should use ClientSession for AggregationOperation'() {
         given: