diff --git a/docs/api-output.md b/docs/api-output.md
index 1cc0b887..8d997fdb 100644
--- a/docs/api-output.md
+++ b/docs/api-output.md
@@ -549,6 +549,10 @@ Use a `.zip` or `.szi` file extension with `toFile` to write to a compressed arc
 
 The container will be set to `zip` when the output is a Buffer or Stream, otherwise it will default to `fs`.
 
+Requires libvips compiled with support for libgsf.
+The prebuilt binaries do not include this - see
+[installing a custom libvips](https://sharp.pixelplumbing.com/install#custom-libvips).
+
 
 **Throws**:
 
diff --git a/lib/output.js b/lib/output.js
index 3825d044..d9263dfe 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -1056,6 +1056,10 @@ function raw (options) {
  *
  * The container will be set to `zip` when the output is a Buffer or Stream, otherwise it will default to `fs`.
  *
+ * Requires libvips compiled with support for libgsf.
+ * The prebuilt binaries do not include this - see
+ * {@link https://sharp.pixelplumbing.com/install#custom-libvips installing a custom libvips}.
+ *
  * @example
  *  sharp('input.tiff')
  *   .png()