diff --git a/redo/windows/button.c b/redo/windows/button.c
index 9233415c..19ef01bc 100644
--- a/redo/windows/button.c
+++ b/redo/windows/button.c
@@ -8,7 +8,7 @@ struct button {
 	void *onClickedData;
 };
 
-static BOOL onWM_COMMAND(uiControl *c, WORD code, LRESULT *lResult)
+static BOOL onWM_COMMAND(uiControl *c, HWND hwnd, WORD code, LRESULT *lResult)
 {
 	struct button *b = (struct button *) c;
 
diff --git a/redo/windows/checkbox.c b/redo/windows/checkbox.c
index cbdbb28b..c9728ee5 100644
--- a/redo/windows/checkbox.c
+++ b/redo/windows/checkbox.c
@@ -8,7 +8,7 @@ struct checkbox {
 	void *onToggledData;
 };
 
-static BOOL onWM_COMMAND(uiControl *cc, WORD code, LRESULT *lResult)
+static BOOL onWM_COMMAND(uiControl *cc, HWND hwnd, WORD code, LRESULT *lResult)
 {
 	struct checkbox *c = (struct checkbox *) cc;
 	WPARAM check;
diff --git a/redo/windows/entry.c b/redo/windows/entry.c
index ccf6cf7b..279203c7 100644
--- a/redo/windows/entry.c
+++ b/redo/windows/entry.c
@@ -9,7 +9,7 @@ struct entry {
 	BOOL inhibitChanged;
 };
 
-static BOOL onWM_COMMAND(uiControl *c, WORD code, LRESULT *lResult)
+static BOOL onWM_COMMAND(uiControl *c, HWND hwnd, WORD code, LRESULT *lResult)
 {
 	struct entry *e = (struct entry *) c;
 
diff --git a/redo/windows/events.c b/redo/windows/events.c
index 24e618ba..445aff40 100644
--- a/redo/windows/events.c
+++ b/redo/windows/events.c
@@ -5,21 +5,21 @@
 
 struct commandHandler {
 	HWND hwnd;
-	BOOL (*handler)(uiControl *, WORD, LRESULT *);
+	BOOL (*handler)(uiControl *, HWND, WORD, LRESULT *);
 	uiControl *c;
 	UT_hash_handle hh;
 };
 
 struct notifyHandler {
 	HWND hwnd;
-	BOOL (*handler)(uiControl *, NMHDR *, LRESULT *);
+	BOOL (*handler)(uiControl *, HWND, NMHDR *, LRESULT *);
 	uiControl *c;
 	UT_hash_handle hh;
 };
 
 struct hscrollHandler {
 	HWND hwnd;
-	BOOL (*handler)(uiControl *, WORD, LRESULT *);
+	BOOL (*handler)(uiControl *, HWND, WORD, LRESULT *);
 	uiControl *c;
 	UT_hash_handle hh;
 };
@@ -41,9 +41,9 @@ struct hscrollHandler *hscrollHandlers = NULL;
 		ch->c = c; \
 		HASH_ADD_PTR(message ## Handlers, hwnd, ch); \
 	}
-REGFN(WM_COMMAND, command, (uiControl *, WORD, LRESULT *))
-REGFN(WM_NOTIFY, notify, (uiControl *, NMHDR *, LRESULT *))
-REGFN(WM_HSCROLL, hscroll, (uiControl *, WORD, LRESULT *))
+REGFN(WM_COMMAND, command, (uiControl *, HWND, WORD, LRESULT *))
+REGFN(WM_NOTIFY, notify, (uiControl *, HWND, NMHDR *, LRESULT *))
+REGFN(WM_HSCROLL, hscroll, (uiControl *, HWND, WORD, LRESULT *))
 
 #define UNREGFN(WM_MESSAGE, message) \
 	void uiWindowsUnregister ## WM_MESSAGE ## Handler(HWND hwnd) \
@@ -59,7 +59,7 @@ UNREGFN(WM_COMMAND, command)
 UNREGFN(WM_NOTIFY, notify)
 UNREGFN(WM_HSCROLL, hscroll)
 
-#define RUNFN(WM_MESSAGE, message, gethwnd, arg2) \
+#define RUNFN(WM_MESSAGE, message, gethwnd, arg3) \
 	BOOL run ## WM_MESSAGE(WPARAM wParam, LPARAM lParam, LRESULT *lResult) \
 	{ \
 		HWND control; \
@@ -70,7 +70,7 @@ UNREGFN(WM_HSCROLL, hscroll)
 		if (control != NULL && IsChild(utilWindow, control) == 0) { \
 			HASH_FIND_PTR(message ## Handlers, &control, ch); \
 			if (ch != NULL) \
-				return (*(ch->handler))(ch->c, arg2, lResult); \
+				return (*(ch->handler))(ch->c, control, arg3, lResult); \
 			/* not registered; fall out to return FALSE */ \
 		} \
 		return FALSE; \
diff --git a/redo/windows/slider.c b/redo/windows/slider.c
index 151cb5b6..52af51c6 100644
--- a/redo/windows/slider.c
+++ b/redo/windows/slider.c
@@ -13,7 +13,7 @@ struct slider {
 	void *onChangedData;
 };
 
-static BOOL onWM_HSCROLL(uiControl *c, WORD code, LRESULT *lResult)
+static BOOL onWM_HSCROLL(uiControl *c, HWND hwnd, WORD code, LRESULT *lResult)
 {
 	struct slider *s = (struct slider *) c;
 
diff --git a/redo/windows/spinbox.c b/redo/windows/spinbox.c
index 4fc7b310..b444b1b4 100644
--- a/redo/windows/spinbox.c
+++ b/redo/windows/spinbox.c
@@ -33,7 +33,7 @@ static intmax_t value(struct spinbox *s)
 
 // control implementation
 
-static BOOL onWM_COMMAND(uiControl *c, WORD code, LRESULT *lResult)
+static BOOL onWM_COMMAND(uiControl *c, HWND hwnd, WORD code, LRESULT *lResult)
 {
 	struct spinbox *s = (struct spinbox *) c;
 
diff --git a/redo/windows/tab.c b/redo/windows/tab.c
index 3eefa75f..cab777f6 100644
--- a/redo/windows/tab.c
+++ b/redo/windows/tab.c
@@ -41,7 +41,7 @@ static void showHidePage(struct tab *t, LRESULT which, int hide)
 
 // control implementation
 
-static BOOL onWM_NOTIFY(uiControl *c, NMHDR *nm, LRESULT *lResult)
+static BOOL onWM_NOTIFY(uiControl *c, HWND hwnd, NMHDR *nm, LRESULT *lResult)
 {
 	struct tab *t = (struct tab *) c;
 
diff --git a/redo/windows/uipriv_windows.h b/redo/windows/uipriv_windows.h
index 0c921f83..c7ad1a55 100644
--- a/redo/windows/uipriv_windows.h
+++ b/redo/windows/uipriv_windows.h
@@ -111,9 +111,9 @@ extern void tabLeaveTabNavigation(HWND);
 
 // events.c
 // TODO split the uiWindows ones to ui_windows.h
-extern void uiWindowsRegisterWM_COMMANDHandler(HWND, BOOL (*)(uiControl *, WORD, LRESULT *), uiControl *);
-extern void uiWindowsRegisterWM_NOTIFYHandler(HWND, BOOL (*)(uiControl *, NMHDR *, LRESULT *), uiControl *);
-extern void uiWindowsRegisterWM_HSCROLLHandler(HWND, BOOL (*)(uiControl *, WORD, LRESULT *), uiControl *);
+extern void uiWindowsRegisterWM_COMMANDHandler(HWND, BOOL (*)(uiControl *, HWND, WORD, LRESULT *), uiControl *);
+extern void uiWindowsRegisterWM_NOTIFYHandler(HWND, BOOL (*)(uiControl *, HWND, NMHDR *, LRESULT *), uiControl *);
+extern void uiWindowsRegisterWM_HSCROLLHandler(HWND, BOOL (*)(uiControl *, HWND, WORD, LRESULT *), uiControl *);
 extern void uiWindowsUnregisterWM_COMMANDHandler(HWND);
 extern void uiWindowsUnregisterWM_NOTIFYHandler(HWND);
 extern void uiWindowsUnregisterWM_HSCROLLHandler(HWND);