diff --git a/README.md b/README.md
index 93ac8a49..854cd2b2 100644
--- a/README.md
+++ b/README.md
@@ -83,6 +83,10 @@ libvips must have `build-essential`, `pkg-config`, `libglib2.0-dev`,
 `libexpat1-dev`.  See the **Dependencies** section below for a full list
 of the libvips optional dependencies.
 
+libvips uses the GObject introspection mechanism by default, so you'll need
+packages like `libgirepository1.0-dev`. Use `-Dintrospection=false` to
+disable introspection support.
+
 There are basic bash completions in `completions/`, see the README in there.
 
 ## Cheatsheet