diff --git a/src/ol/source/Vector.js b/src/ol/source/Vector.js
index e44191b9fa..c72f777bbe 100644
--- a/src/ol/source/Vector.js
+++ b/src/ol/source/Vector.js
@@ -282,6 +282,9 @@ class VectorSource extends Source {
    * instead. A feature will not be added to the source if feature with
    * the same id is already there. The reason for this behavior is to avoid
    * feature duplication when using bbox or tile loading strategies.
+   * Note: this also applies if an {@link module:ol/Collection} is used for features,
+   * meaning that if a feature with a duplicate id is added in the collection, it will
+   * be removed from it right away.
    * @param {import("../Feature.js").default} feature Feature to add.
    * @api
    */
@@ -300,6 +303,9 @@ class VectorSource extends Source {
     const featureKey = getUid(feature);
 
     if (!this.addToIndex_(featureKey, feature)) {
+      if (this.featuresCollection_) {
+        this.featuresCollection_.remove(feature);
+      }
       return;
     }
 
diff --git a/test/spec/ol/source/vector.test.js b/test/spec/ol/source/vector.test.js
index 0223cec14f..d48d2962a3 100644
--- a/test/spec/ol/source/vector.test.js
+++ b/test/spec/ol/source/vector.test.js
@@ -719,6 +719,19 @@ describe('ol.source.Vector', function() {
       expect(source.getFeatures().length).to.be(0);
     });
 
+    it('prevents adding two features with a duplicate id in the collection', function() {
+      source = new VectorSource({
+        features: new Collection()
+      });
+      const feature1 = new Feature();
+      feature1.setId('1');
+      const feature2 = new Feature();
+      feature2.setId('1');
+      const collection = source.getFeaturesCollection();
+      collection.push(feature1);
+      collection.push(feature2);
+      expect(collection.getLength()).to.be(1);
+    });
   });
 
   describe('with a collection of features plus spatial index', function() {