diff --git a/dialog_darwin.go b/dialog_darwin.go
index 6ce28c0..421e838 100644
--- a/dialog_darwin.go
+++ b/dialog_darwin.go
@@ -31,10 +31,10 @@ func _msgBox(parent *Window, primarytext string, secondarytext string, style uin
 	}
 	switch style {
 	case 0: // normal
-		C.msgBox(pwin, primary, secondary, nil)
+		C.msgBox(pwin, primary, secondary)
 		return OK
 	case 1: // error
-		C.msgBoxError(pwin, primary, secondary, nil)
+		C.msgBoxError(pwin, primary, secondary)
 		return OK
 	}
 	panic(fmt.Errorf("unknown message box style %d\n", style))
diff --git a/dialog_darwin.m b/dialog_darwin.m
index 7f72d02..10a5f26 100644
--- a/dialog_darwin.m
+++ b/dialog_darwin.m
@@ -9,7 +9,7 @@
 #define to(T, x) ((T *) (x))
 #define toNSWindow(x) to(NSWindow, (x))
 
-static void alert(id parent, NSString *primary, NSString *secondary, NSAlertStyle style, void *chan)
+static void alert(id parent, NSString *primary, NSString *secondary, NSAlertStyle style)
 {
 	NSAlert *box;
 
@@ -23,20 +23,22 @@ static void alert(id parent, NSString *primary, NSString *secondary, NSAlertStyl
 	if (parent == nil)
 		return (intptr_t) [box runModal];
 	else {
+		NSInteger *ret;
+
 		[box beginSheetModalForWindow:toNSWindow(parent)
 			modalDelegate:[NSApp delegate]
 			didEndSelector:@selector(alertDidEnd:returnCode:contextInfo:)
-			contextInfo:chan];
+			contextInfo:&ret];
 		// TODO
 	}
 }
 
-void msgBox(id parent, id primary, id secondary, void *chan)
+void msgBox(id parent, id primary, id secondary)
 {
-	alert(parent, (NSString *) primary, (NSString *) secondary, NSInformationalAlertStyle, chan);
+	alert(parent, (NSString *) primary, (NSString *) secondary, NSInformationalAlertStyle);
 }
 
-void msgBoxError(id parent, id primary, id secondary, void *chan)
+void msgBoxError(id parent, id primary, id secondary)
 {
-	alert(parent, (NSString *) primary, (NSString *) secondary, NSCriticalAlertStyle, chan);
+	alert(parent, (NSString *) primary, (NSString *) secondary, NSCriticalAlertStyle);
 }
diff --git a/objc_darwin.h b/objc_darwin.h
index 22bafb1..8174ec1 100644
--- a/objc_darwin.h
+++ b/objc_darwin.h
@@ -68,8 +68,8 @@ extern void breakMainLoop(void);
 extern void cocoaMainLoop(void);
 
 /* dialog_darwin.m */
-extern void msgBox(id, id, id, void *);
-extern void msgBoxError(id, id, id, void *);
+extern void msgBox(id, id, id);
+extern void msgBoxError(id, id, id);
 
 /* listbox_darwin.m */
 extern id toListboxItem(id, id);