diff --git a/src/ol/Collection.js b/src/ol/Collection.js
index d84f62311b..bf5f0f9183 100644
--- a/src/ol/Collection.js
+++ b/src/ol/Collection.js
@@ -26,7 +26,7 @@ export class CollectionEvent extends Event {
   /**
    * @param {CollectionEventType} type Type.
    * @param {*=} opt_element Element.
-   * @param {number} opt_index The index of the added or removed element.
+   * @param {number=} opt_index The index of the added or removed element.
    */
   constructor(type, opt_element, opt_index) {
     super(type);
diff --git a/src/ol/format/IIIFInfo.js b/src/ol/format/IIIFInfo.js
index 8a3bd27bd5..b2cb1fa5e9 100644
--- a/src/ol/format/IIIFInfo.js
+++ b/src/ol/format/IIIFInfo.js
@@ -349,7 +349,7 @@ class IIIFInfo {
   }
 
   /**
-   * @param {PreferredOptions} opt_preferredOptions Optional options for preferred format and quality.
+   * @param {PreferredOptions=} opt_preferredOptions Optional options for preferred format and quality.
    * @returns {import("../source/IIIF.js").Options} IIIF tile source ready constructor options.
    * @api
    */
diff --git a/src/ol/renderer/canvas/VectorLayer.js b/src/ol/renderer/canvas/VectorLayer.js
index 9c79bcb177..591ea95f83 100644
--- a/src/ol/renderer/canvas/VectorLayer.js
+++ b/src/ol/renderer/canvas/VectorLayer.js
@@ -457,7 +457,7 @@ class CanvasVectorLayerRenderer extends CanvasLayerRenderer {
    * @param {number} squaredTolerance Squared render tolerance.
    * @param {import("../../style/Style.js").default|Array<import("../../style/Style.js").default>} styles The style or array of styles.
    * @param {import("../../render/canvas/BuilderGroup.js").default} builderGroup Builder group.
-   * @param {import("../../proj.js").TransformFunction} opt_transform Transform from user to view projection.
+   * @param {import("../../proj.js").TransformFunction=} opt_transform Transform from user to view projection.
    * @return {boolean} `true` if an image is loading.
    */
   renderFeature(feature, squaredTolerance, styles, builderGroup, opt_transform) {
diff --git a/src/ol/rotationconstraint.js b/src/ol/rotationconstraint.js
index 3da582e459..aad13c3724 100644
--- a/src/ol/rotationconstraint.js
+++ b/src/ol/rotationconstraint.js
@@ -71,7 +71,7 @@ export function createSnapToZero(opt_tolerance) {
   return (
     /**
      * @param {number|undefined} rotation Rotation.
-     * @param {boolean} opt_isMoving True if an interaction or animation is in progress.
+     * @param {boolean=} opt_isMoving True if an interaction or animation is in progress.
      * @return {number|undefined} Rotation.
      */
     function(rotation, opt_isMoving) {
diff --git a/src/ol/source/IIIF.js b/src/ol/source/IIIF.js
index 8370a936f3..9f28e3a1f2 100644
--- a/src/ol/source/IIIF.js
+++ b/src/ol/source/IIIF.js
@@ -59,7 +59,7 @@ function formatPercentage(percentage) {
 class IIIF extends TileImage {
 
   /**
-   * @param {Options} opt_options Tile source options. Use {@link import("../format/IIIFInfo.js").IIIFInfo}
+   * @param {Options=} opt_options Tile source options. Use {@link import("../format/IIIFInfo.js").IIIFInfo}
    * to parse Image API service information responses into constructor options.
    * @api
    */