diff --git a/titlebar.c.v b/titlebar.c.v
index 8bc201f..a8a7a31 100644
--- a/titlebar.c.v
+++ b/titlebar.c.v
@@ -22,6 +22,10 @@ fn C.DwmSetWindowAttribute(voidptr, u32, &u8, u32)
 // titlebar_dark set the window titlebar to be dark or light, api is from dwmapi.h, windows 10+ only
 pub fn titlebar_dark(dark bool) {
 	$if windows {
-		C.DwmSetWindowAttribute(sapp.win32_get_hwnd(), 20, &dark, sizeof(dark))
+		// set_theme() can run before sapp.run(); win32_get_hwnd() then
+		// aborts on `_sapp.valid`. Guard with isvalid().
+		if sapp.isvalid() {
+			C.DwmSetWindowAttribute(sapp.win32_get_hwnd(), 20, &dark, sizeof(dark))
+		}
 	}
 }