diff --git a/mpv.py b/mpv.py
index 831a813..c64f735 100644
--- a/mpv.py
+++ b/mpv.py
@@ -308,7 +308,7 @@ class MpvEventClientMessage(Structure):
 WakeupCallback = CFUNCTYPE(None, c_void_p)
 
 OpenGlCbUpdateFn = CFUNCTYPE(None, c_void_p)
-OpenGlCbGetProcAddrFn = CFUNCTYPE(None, c_void_p, c_char_p)
+OpenGlCbGetProcAddrFn = CFUNCTYPE(c_void_p, c_void_p, c_char_p)
 
 def _handle_func(name, args, restype, errcheck, ctx=MpvHandle):
     func = getattr(backend, name)