diff --git a/src/ol/source/Raster.js b/src/ol/source/Raster.js
index 100698291e..6f488215eb 100644
--- a/src/ol/source/Raster.js
+++ b/src/ol/source/Raster.js
@@ -113,7 +113,8 @@ inherits(RasterSourceEvent, Event);
 
 /**
  * @typedef {Object} Options
- * @property {Array.<module:ol/source/Source|module:ol/layer/Layer>} sources Input sources or layers.
+ * @property {Array.<module:ol/source/Source|module:ol/layer/Layer>} sources Input
+ * sources or layers. Vector layers must be configured with `renderMode: 'image'`.
  * @property {module:ol/source/Raster~Operation} [operation] Raster operation.
  * The operation will be called with data from input sources
  * and the output will be assigned to the raster source.