diff --git a/pyvips/vdecls.py b/pyvips/vdecls.py
index 547debb..d142268 100644
--- a/pyvips/vdecls.py
+++ b/pyvips/vdecls.py
@@ -72,8 +72,8 @@ def cdefs(features):
         const char* g_type_name (GType gtype);
         GType g_type_from_name (const char* name);
 
-        typedef ... VipsTypeMap2Fn;
-        void* vips_type_map (GType base, VipsTypeMap2Fn fn, void* a, void* b);
+        typedef void* (*VipsTypeMap2Fn) (GType type, void* a, void* b);
+        void* vips_type_map (GType base, void* fn, void* a, void* b);
 
         const char* vips_error_buffer (void);
         void vips_error_clear (void);