diff --git a/docs/api-constructor.md b/docs/api-constructor.md
index f13ad181..140d3c7c 100644
--- a/docs/api-constructor.md
+++ b/docs/api-constructor.md
@@ -55,7 +55,7 @@ sharp({
     width: 300,
     height: 200,
     channels: 4,
-    background: { r: 255, g: 0, b: 0, alpha: 128 }
+    background: { r: 255, g: 0, b: 0, alpha: 0.5 }
   }
 })
 .png()
diff --git a/lib/constructor.js b/lib/constructor.js
index 60f1de7c..8d27d761 100644
--- a/lib/constructor.js
+++ b/lib/constructor.js
@@ -81,7 +81,7 @@ const debuglog = util.debuglog('sharp');
  *     width: 300,
  *     height: 200,
  *     channels: 4,
- *     background: { r: 255, g: 0, b: 0, alpha: 128 }
+ *     background: { r: 255, g: 0, b: 0, alpha: 0.5 }
  *   }
  * })
  * .png()