diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,6 +1,10 @@
+### 2.0.18
+
++ The `parameter` parameter for the [`activate`](https://hackage.haskell.org/package/gi-gio-2.0.18/docs/GI-Gio-Callbacks.html#t:ActionEntryActivateFieldCallback) callback of `ActionEntry` is nullable, but it is not marked as such in the introspection data.
+
 ### 2.0.17
 
-+ The return of [`applicationNew`](https://hackage.haskell.org/package/gi-gio/docs/GI-Gio-Objects-Application.html#v:applicationNew) value can be null, but it is not marked as such in the introspection data, leading to a rather confusing error message (see [issue 142](https://github.com/haskell-gi/haskell-gi/issues/142) and [issue 143](https://github.com/haskell-gi/haskell-gi/issues/143)).
++ The return value of [`applicationNew`](https://hackage.haskell.org/package/gi-gio/docs/GI-Gio-Objects-Application.html#v:applicationNew) can be null, but it is not marked as such in the introspection data, leading to a rather confusing error message (see [issue 142](https://github.com/haskell-gi/haskell-gi/issues/142) and [issue 143](https://github.com/haskell-gi/haskell-gi/issues/143)).
 
 ### 2.0.16
 
diff --git a/Gio.overrides b/Gio.overrides
--- a/Gio.overrides
+++ b/Gio.overrides
@@ -23,6 +23,10 @@
 # https://github.com/haskell-gi/haskell-gi/issues/143
 set-attr Gio/Application/new/@return-value nullable 1
 
+# The 'parameter' parameter for the activate callback is nullable, but
+# it is not marked as such in the introspection data.
+set-attr Gio/ActionEntry/activate/activate/@parameters/parameter nullable 1
+
 # Not supported on Windows.
 if windows
    ignore DBusMessage.get_unix_fd_list
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # Documentation
 Autogenerated documentation for this package can be found at
 
-[https://hackage.haskell.org/package/gi-gio-2.0.17/docs/GI-Gio.html](https://hackage.haskell.org/package/gi-gio-2.0.17/docs/GI-Gio.html)
+[https://hackage.haskell.org/package/gi-gio-2.0.18/docs/GI-Gio.html](https://hackage.haskell.org/package/gi-gio-2.0.18/docs/GI-Gio.html)
 
 For general documentation on using [haskell-gi](https://github.com/haskell-gi/haskell-gi) based bindings, see [the project page](https://github.com/haskell-gi/haskell-gi) or [the Wiki](https://github.com/haskell-gi/haskell-gi/wiki).
diff --git a/gi-gio.cabal b/gi-gio.cabal
--- a/gi-gio.cabal
+++ b/gi-gio.cabal
@@ -1,5 +1,5 @@
 name:                 gi-gio
-version:              2.0.17
+version:              2.0.18
 synopsis:             Gio bindings
 description:          Bindings for Gio, autogenerated by haskell-gi.
 homepage:             https://github.com/haskell-gi/haskell-gi