diff --git a/src/widget/opengl.c b/src/widget/opengl.c
index d75b358..50fb747 100644
--- a/src/widget/opengl.c
+++ b/src/widget/opengl.c
@@ -381,7 +381,7 @@ static void mwOpenGLMakeCurrentImpl(MwWidget handle) {
 #ifdef USE_GDI
 	if(handle->lowlevel->common.type == MwLLBackendGDI) {
 		gdiopengl_t* o		       = handle->internal;
-		void (*swap_interval_ext)(int) = NULL;
+		int (__stdcall *swap_interval_ext)(int) = NULL;
 
 		o->wglMakeCurrent(o->dc, o->gl);