diff --git a/samples/NetVips.Samples/Samples/GenerateImageClass.cs b/samples/NetVips.Samples/Samples/GenerateImageClass.cs
index 847963ba..ce4b0e14 100644
--- a/samples/NetVips.Samples/Samples/GenerateImageClass.cs
+++ b/samples/NetVips.Samples/Samples/GenerateImageClass.cs
@@ -776,12 +776,13 @@ private string Generate(string indent = "        ")
             // remove operations we have to wrap by hand
             var exclude = new[]
             {
-                "scale",
-                "ifthenelse",
+                "addalpha",
                 "bandjoin",
                 "bandrank",
+                "case",
                 "composite",
-                "case"
+                "ifthenelse",
+                "scale"
             };
 
             // get the list of all nicknames we can generate docstrings for.
diff --git a/src/NetVips/Image.cs b/src/NetVips/Image.cs
index d7ac389f..9ba52d9a 100644
--- a/src/NetVips/Image.cs
+++ b/src/NetVips/Image.cs
@@ -2036,7 +2036,7 @@ public Image AddAlpha()
             // use `vips_addalpha` on libvips >= 8.6.
             if (NetVips.AtLeastLibvips(8, 6))
             {
-                var result = VipsImage.AddAlpha(this, out var vi);
+                var result = VipsImage.AddAlpha(this, out var vi, IntPtr.Zero);
                 if (result != 0)
                 {
                     throw new VipsException("unable to append alpha channel to image.");
diff --git a/src/NetVips/Internal/Vips.cs b/src/NetVips/Internal/Vips.cs
index 4f28f4a5..085542da 100644
--- a/src/NetVips/Internal/Vips.cs
+++ b/src/NetVips/Internal/Vips.cs
@@ -451,7 +451,7 @@ internal static extern IntPtr NewFromMemoryCopy(IntPtr data, UIntPtr size, int w
         [SuppressUnmanagedCodeSecurity]
         [DllImport(Libraries.Vips, CallingConvention = CallingConvention.Cdecl,
             EntryPoint = "vips_addalpha")]
-        internal static extern int AddAlpha(Image image, out IntPtr @out);
+        internal static extern int AddAlpha(Image image, out IntPtr @out, IntPtr args);
 
         [SuppressUnmanagedCodeSecurity]
         [DllImport(Libraries.Vips, CallingConvention = CallingConvention.Cdecl,