diff --git a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java
index 733ca07ee..795464704 100644
--- a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java
+++ b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java
@@ -2536,15 +2536,18 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @param savedObject
 	 * @param id
 	 */
+	@SuppressWarnings("unchecked")
 	protected void populateIdIfNecessary(Object savedObject, Object id) {
 
 		if (id == null) {
 			return;
 		}
 
-		if (savedObject instanceof Document) {
-			Document document = (Document) savedObject;
-			document.put(ID_FIELD, id);
+		if (savedObject instanceof Map) {
+
+			Map<String, Object> map = (Map<String, Object>) savedObject;
+			map.put(ID_FIELD, id);
+
 			return;
 		}
 
diff --git a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveMongoTemplate.java b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveMongoTemplate.java
index b73fbdce7..f4573da75 100644
--- a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveMongoTemplate.java
+++ b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveMongoTemplate.java
@@ -2224,15 +2224,18 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 * @param savedObject
 	 * @param id
 	 */
+	@SuppressWarnings("unchecked")
 	private void populateIdIfNecessary(Object savedObject, @Nullable Object id) {
 
 		if (id == null) {
 			return;
 		}
 
-		if (savedObject instanceof Document) {
-			Document Document = (Document) savedObject;
-			Document.put(ID_FIELD, id);
+		if (savedObject instanceof Map) {
+
+			Map<String, Object> map = (Map<String, Object>) savedObject;
+			map.put(ID_FIELD, id);
+
 			return;
 		}
 
diff --git a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MongoTemplateUnitTests.java b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MongoTemplateUnitTests.java
index 28c3b6072..1c7be8931 100644
--- a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MongoTemplateUnitTests.java
+++ b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MongoTemplateUnitTests.java
@@ -26,7 +26,9 @@ import lombok.Data;
 
 import java.math.BigInteger;
 import java.util.Collections;
+import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import java.util.regex.Pattern;
 
@@ -218,6 +220,19 @@ public class MongoTemplateUnitTests extends MongoOperationsUnitTests {
 		assertThat(entity.id, is(notNullValue()));
 	}
 
+	@Test // DATAMONGO-1912
+	public void autogeneratesIdForMap() {
+
+		MongoTemplate template = spy(this.template);
+		doReturn(new ObjectId()).when(template).saveDocument(Mockito.any(String.class), Mockito.any(Document.class),
+				Mockito.any(Class.class));
+
+		Map<String, String> entity = new LinkedHashMap<>();
+		template.save(entity, "foo");
+
+		assertThat(entity, hasKey("_id"));
+	}
+
 	@Test // DATAMONGO-374
 	public void convertsUpdateConstraintsUsingConverters() {
 
diff --git a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/ReactiveMongoTemplateUnitTests.java b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/ReactiveMongoTemplateUnitTests.java
index 06f445430..720e3c519 100644
--- a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/ReactiveMongoTemplateUnitTests.java
+++ b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/ReactiveMongoTemplateUnitTests.java
@@ -21,7 +21,11 @@ import static org.mockito.Mockito.*;
 import static org.mockito.Mockito.any;
 import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
 
+import java.util.LinkedHashMap;
+import java.util.Map;
+
 import lombok.Data;
+import org.bson.types.ObjectId;
 import reactor.core.publisher.Mono;
 
 import org.bson.Document;
@@ -57,6 +61,7 @@ import com.mongodb.reactivestreams.client.FindPublisher;
 import com.mongodb.reactivestreams.client.MongoClient;
 import com.mongodb.reactivestreams.client.MongoCollection;
 import com.mongodb.reactivestreams.client.MongoDatabase;
+import reactor.test.StepVerifier;
 
 /**
  * Unit tests for {@link ReactiveMongoTemplate}.
@@ -117,6 +122,20 @@ public class ReactiveMongoTemplateUnitTests {
 		assertTrue(ReflectionTestUtils.getField(template, "mongoConverter") instanceof MappingMongoConverter);
 	}
 
+	@Test // DATAMONGO-1912
+	public void autogeneratesIdForMap() {
+
+		ReactiveMongoTemplate template = spy(this.template);
+		doReturn(Mono.just(new ObjectId())).when(template).saveDocument(Mockito.any(String.class), Mockito.any(Document.class),
+				Mockito.any(Class.class));
+
+		Map<String, String> entity = new LinkedHashMap<>();
+		StepVerifier.create(template.save(entity, "foo")).consumeNextWith(actual -> {
+
+			assertThat(entity, hasKey("_id"));
+		}).verifyComplete();
+	}
+
 	@Test // DATAMONGO-1518
 	public void findShouldUseCollationWhenPresent() {