diff --git a/externs/olx.js b/externs/olx.js
index 3ccd3c2fb6..59dd0793f9 100644
--- a/externs/olx.js
+++ b/externs/olx.js
@@ -4184,7 +4184,8 @@ olx.source.ImageMapGuideOptions.prototype.projection;
 
 /**
  * Ratio. `1` means image requests are the size of the map viewport, `2` means
- * twice the size of the map viewport, and so on. Default is `1`.
+ * twice the width and height of the map viewport, and so on. Must be `1` or 
+ * higher. Default is `1`.
  * @type {number|undefined}
  * @api stable
  */
@@ -4402,7 +4403,8 @@ olx.source.ImageCanvasOptions.prototype.projection;
 
 /**
  * Ratio. 1 means canvases are the size of the map viewport, 2 means twice the
- * size of the map viewport, and so on. Default is `1.5`.
+ * width and height of the map viewport, and so on. Must be `1` or higher.
+ * Default is `1.5`.
  * @type {number|undefined}
  * @api
  */
@@ -4465,7 +4467,8 @@ olx.source.ImageVectorOptions.prototype.projection;
 
 /**
  * Ratio. 1 means canvases are the size of the map viewport, 2 means twice the
- * size of the map viewport, and so on. Default is `1.5`.
+ * width and height of the map viewport, and so on. Must be `1` or higher. 
+ * Default is `1.5`.
  * @type {number|undefined}
  * @api
  */
@@ -4589,7 +4592,8 @@ olx.source.ImageWMSOptions.prototype.projection;
 
 /**
  * Ratio. `1` means image requests are the size of the map viewport, `2` means
- * twice the size of the map viewport, and so on. Default is `1.5`.
+ * twice the width and height of the map viewport, and so on. Must be `1` or 
+ * higher. Default is `1.5`.
  * @type {number|undefined}
  * @api stable
  */