diff --git a/redo/dialog.go b/redo/dialog.go
index 877ccf2..1567cc7 100644
--- a/redo/dialog.go
+++ b/redo/dialog.go
@@ -2,10 +2,19 @@
 
 package ui
 
-// OpenFile opens a dialog box that asks the user to choose a file.
-// It returns the selected filename, or an empty string if no file was chosen.
-// All events stop while OpenFile is executing. (TODO move to doc.go)
-// If possible on a given system, OpenFile() will not dereference links; it will return the link file itself.
-func OpenFile() (filename string) {
-	return openFile()
+type windowDialog interface {
+	openFile(f func(filename string))
+}
+
+// OpenFile opens a dialog box that asks the user to choose a file.
+// The dialog box is modal to win, which mut not be nil.
+// Some time after the dialog box is closed, OpenFile runs f on the main thread, passing filename.
+// filename is the selected filename, or an empty string if no file was chosen.
+// OpenFile does not ensure that f remains alive; the programmer is responsible for this.
+// If possible on a given system, OpenFile() will not dereference links; it will return the link file itself.
+func OpenFile(win Window, f func(filename string)) {
+	if win == nil {
+		panic("Window passed to OpenFile() cannot be nil")
+	}
+	win.openFile(f)
 }
diff --git a/redo/dialog_windows.c b/redo/dialog_windows.c
index ad48cd5..10fb75c 100644
--- a/redo/dialog_windows.c
+++ b/redo/dialog_windows.c
@@ -3,73 +3,60 @@
 #include "winapi_windows.h"
 #include "_cgo_export.h"
 
-static LRESULT CALLBACK dialogSubProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR id, DWORD_PTR data)
-{
-	switch (uMsg) {
-	case WM_COMMAND:
-		// we must re-enable other windows in the right order (see http://blogs.msdn.com/b/oldnewthing/archive/2004/02/27/81155.aspx)
-		// see http://stackoverflow.com/questions/25494914/is-there-something-like-cdn-filecancel-analogous-to-cdn-fileok-for-getting-when
-		if (HIWORD(wParam) == BN_CLICKED && LOWORD(wParam) == IDCANCEL)
-				SendMessageW(msgwin, msgEndModal, 0, 0);
-		break;		// let the dialog handle it now
-	case WM_NCDESTROY:
-		if ((*fv_RemoveWindowSubclass)(hwnd, dialogSubProc, id) == FALSE)
-			xpanic("error removing dialog subclass (which was for its own event handler)", GetLastError());
-	}
-	return (*fv_DefSubclassProc)(hwnd, uMsg, wParam, lParam);
-}
-
 // this should be reasonable
 #define NFILENAME 4096
 
-static UINT_PTR CALLBACK openSaveFileHook(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
-{
-	if (uMsg == WM_INITDIALOG) {
-		HWND parent;
-
-		parent = GetParent(hwnd);
-		if (parent == NULL)
-			xpanic("error gettign parent of OpenFile() dialog for event handling", GetLastError());
-		if ((*fv_SetWindowSubclass)(parent, dialogSubProc, 0, (DWORD_PTR) NULL) == FALSE)
-			xpanic("error subclassing OpenFile() dialog to give it its own event handler", GetLastError());
-	} else if (uMsg == WM_NOTIFY) {
-		OFNOTIFY *of = (OFNOTIFY *) lParam;
-
-		if (of->hdr.code == CDN_FILEOK)
-			SendMessageW(msgwin, msgEndModal, 0, 0);
-	}
-	return 0;
-}
-
-WCHAR *openFile(void)
+struct openFileData {
+	HWND parent;
+	void *f;
+	WCHAR *filenameBuffer;
+};
+
+static DWORD WINAPI doOpenFile(LPVOID data)
 {
+	struct openFileData *o = (struct openFileData *) data;
 	OPENFILENAMEW ofn;
 	DWORD err;
-	WCHAR *filenameBuffer;
 
-	// freed on the Go side
-	filenameBuffer = (WCHAR *) malloc((NFILENAME + 1) * sizeof (WCHAR));
-	if (filenameBuffer == NULL)
-		xpanic("memory exhausted in OpenFile()", GetLastError());
-	filenameBuffer[0] = L'\0';			// required by GetOpenFileName() to indicate no previous filename
+	o->filenameBuffer[0] = L'\0';			// required by GetOpenFileName() to indicate no previous filename
 	ZeroMemory(&ofn, sizeof (OPENFILENAMEW));
 	ofn.lStructSize = sizeof (OPENFILENAMEW);
-	ofn.hwndOwner = NULL;
+	ofn.hwndOwner = o->parent;
 	ofn.hInstance = hInstance;
 	ofn.lpstrFilter = NULL;			// no filters
-	ofn.lpstrFile = filenameBuffer;
+	ofn.lpstrFile = o->filenameBuffer;
 	ofn.nMaxFile = NFILENAME + 1;	// TODO include + 1?
 	ofn.lpstrInitialDir = NULL;			// let system decide
 	ofn.lpstrTitle = NULL;			// let system decide
 	// TODO OFN_SHAREAWARE?
-	ofn.Flags = OFN_ENABLEHOOK | OFN_EXPLORER | OFN_FILEMUSTEXIST | OFN_FORCESHOWHIDDEN | OFN_HIDEREADONLY | OFN_LONGNAMES | OFN_NOCHANGEDIR | OFN_NODEREFERENCELINKS | OFN_NOTESTFILECREATE | OFN_PATHMUSTEXIST;
-	ofn.lpfnHook = openSaveFileHook;
-	SendMessageW(msgwin, msgBeginModal, 0, 0);
+	ofn.Flags = OFN_EXPLORER | OFN_FILEMUSTEXIST | OFN_FORCESHOWHIDDEN | OFN_HIDEREADONLY | OFN_LONGNAMES | OFN_NOCHANGEDIR | OFN_NODEREFERENCELINKS | OFN_NOTESTFILECREATE | OFN_PATHMUSTEXIST;
 	if (GetOpenFileNameW(&ofn) == FALSE) {
 		err = CommDlgExtendedError();
-		if (err == 0)				// user cancelled
-			return NULL;
-		xpaniccomdlg("error running open file dialog", err);
+		if (err != 0)				// user cancelled
+			xpaniccomdlg("error running open file dialog", err);
+		free(o->filenameBuffer);		// free now so we can set it to NULL without leaking
+		o->filenameBuffer = NULL;
 	}
-	return filenameBuffer;
+	if (PostMessageW(msgwin, msgOpenFileDone, (WPARAM) (o->filenameBuffer), (LPARAM) (o->f)) == 0)
+		xpanic("error posting OpenFile() finished message to message-only window", GetLastError());
+	free(o);		// won't free o->f or o->filenameBuffer in above invocation
+	return 0;
+}
+
+void openFile(HWND hwnd, void *f)
+{
+	struct openFileData *o;
+
+	// freed by the thread
+	o = (struct openFileData *) malloc(sizeof (struct openFileData));
+	if (o == NULL)
+		xpanic("memory exhausted allocating data structure in OpenFile()", GetLastError());
+	o->parent = hwnd;
+	o->f = f;
+	// freed on the Go side
+	o->filenameBuffer = (WCHAR *) malloc((NFILENAME + 1) * sizeof (WCHAR));
+	if (o->filenameBuffer == NULL)
+		xpanic("memory exhausted allocating filename buffer in OpenFile()", GetLastError());
+	if (CreateThread(NULL, 0, doOpenFile, (LPVOID) o, 0, NULL) == NULL)
+		xpanic("error creating thread for running OpenFIle()", GetLastError());
 }
diff --git a/redo/dialog_windows.go b/redo/dialog_windows.go
index 9ea483c..80f7ac6 100644
--- a/redo/dialog_windows.go
+++ b/redo/dialog_windows.go
@@ -9,11 +9,17 @@ import (
 // #include "winapi_windows.h"
 import "C"
 
-func openFile() string {
-	name := C.openFile()
+func (w *window) openFile(f func(filename string)) {
+	C.openFile(w.hwnd, unsafe.Pointer(&f))
+}
+
+//export finishOpenFile
+func finishOpenFile(name *C.WCHAR, fp unsafe.Pointer) {
+	f := (*func(string))(fp)
 	if name == nil {
-		return ""
+		(*f)("")
+		return
 	}
 	defer C.free(unsafe.Pointer(name))
-	return wstrToString(name)
+	(*f)(wstrToString(name))
 }
diff --git a/redo/uitask_windows.c b/redo/uitask_windows.c
index 193b24f..6e5e384 100644
--- a/redo/uitask_windows.c
+++ b/redo/uitask_windows.c
@@ -146,6 +146,9 @@ static LRESULT CALLBACK msgwinproc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM l
 		endModal();
 		EnumThreadWindows(GetCurrentThreadId(), beginEndModalAll, msgEndModal);
 		return 0;
+	case msgOpenFileDone:
+		finishOpenFile((WCHAR *) wParam, (void *) lParam);
+		return 0;
 	default:
 		return DefWindowProcW(hwnd, uMsg, wParam, lParam);
 	}
diff --git a/redo/winapi_windows.h b/redo/winapi_windows.h
index 477a2f0..ca88f01 100644
--- a/redo/winapi_windows.h
+++ b/redo/winapi_windows.h
@@ -40,6 +40,7 @@ enum {
 	msgAreaKeyUp,
 	msgLoadImageList,
 	msgTableMakeInitialCheckboxImageList,
+	msgOpenFileDone,
 };
 
 // uitask_windows.c
@@ -149,6 +150,6 @@ enum {
 extern HIMAGELIST makeCheckboxImageList(HWND, HTHEME *);
 
 // dialog_windows.c
-extern WCHAR *openFile(void);
+extern void openFile(HWND, void *);
 
 #endif
diff --git a/redo/window.go b/redo/window.go
index 0c6391f..d700d14 100644
--- a/redo/window.go
+++ b/redo/window.go
@@ -25,6 +25,8 @@ type Window interface {
 	// If this handler returns true, the Window is closed as defined by Close above.
 	// If this handler returns false, the Window is not closed.
 	OnClosing(func() bool)
+
+	windowDialog
 }
 
 // NewWindow creates a new Window with the given title text, size, and control.
diff --git a/redo/zz_test.go b/redo/zz_test.go
index ab6591e..0afd7d7 100644
--- a/redo/zz_test.go
+++ b/redo/zz_test.go
@@ -75,6 +75,13 @@ func (a *areaHandler) Paint(r image.Rectangle) *image.RGBA {
 func (a *areaHandler) Mouse(me MouseEvent) { fmt.Printf("%#v\n", me) }
 func (a *areaHandler) Key(ke KeyEvent) bool { fmt.Printf("%#v %q\n", ke, ke.Key); return a.handled }
 
+func (tw *testwin) openFile(fn string) {
+	if fn == "" {
+		fn = "<no file selected>"
+	}
+	tw.fnlabel.SetText(fn)
+}
+
 func (tw *testwin) addfe() {
 	tw.festart = NewButton("Start")
 	tw.festart.OnClicked(func() {
@@ -106,11 +113,7 @@ func (tw *testwin) addfe() {
 	})
 	tw.openbtn = NewButton("Open")
 	tw.openbtn.OnClicked(func() {
-		fn := OpenFile()
-		if fn == "" {
-			fn = "<no file selected>"
-		}
-		tw.fnlabel.SetText(fn)
+		OpenFile(tw.w, tw.openFile)
 	})
 	tw.fnlabel = NewStandaloneLabel("<no file selected>")
 	tw.festack = NewVerticalStack(tw.festart, tw.felabel, tw.festop,