diff --git a/types/openlayers/index.d.ts b/types/openlayers/index.d.ts
index 441214cce6..538dedbc9c 100644
--- a/types/openlayers/index.d.ts
+++ b/types/openlayers/index.d.ts
@@ -12620,7 +12620,7 @@ declare module olx {
          *     insertVertexCondition: (ol.EventsConditionType|undefined),
          *     pixelTolerance: (number|undefined),
          *     style: (ol.style.Style|Array.<ol.style.Style>|ol.StyleFunction|undefined),
-         *     features: ol.Collection.<ol.Feature>,
+         *     features: (ol.Collection.<ol.Feature>|undefined),
          *     wrapX: (boolean|undefined),
          *     source: (ol.source.Vector|undefined)}}
          */
@@ -12630,7 +12630,7 @@ declare module olx {
             insertVertexCondition?: ol.EventsConditionType;
             pixelTolerance?: number;
             style?: (ol.style.Style | ol.style.Style[] | ol.StyleFunction);
-            features: ol.Collection<ol.Feature>;
+            features?: ol.Collection<ol.Feature>;
             wrapX?: boolean;
             source?: ol.source.Vector;            
         }
diff --git a/types/openlayers/openlayers-tests.ts b/types/openlayers/openlayers-tests.ts
index 50281ff0fe..f8e9ac91ec 100644
--- a/types/openlayers/openlayers-tests.ts
+++ b/types/openlayers/openlayers-tests.ts
@@ -702,10 +702,16 @@ jsonValue = geojsonFormat.writeGeometryObject(geometry, writeOptions);
 //
 // ol.interactions
 //
-let modify: ol.interaction.Modify = new ol.interaction.Modify({
+let modifyFeature: ol.interaction.Modify = new ol.interaction.Modify({
     insertVertexCondition: ol.events.condition.never,
     features: new ol.Collection<ol.Feature>(featureArray),
 });
+let modifySource: ol.interaction.Modify = new ol.interaction.Modify({
+    insertVertexCondition: ol.events.condition.never,
+    source: new ol.source.Vector({
+        features: new ol.Collection<ol.Feature>(featureArray),
+    }),
+});
 
 let draw: ol.interaction.Draw = new ol.interaction.Draw({
     type: "Point",