diff --git a/src/window.c b/src/window.c
index e56bb638..978f7b88 100644
--- a/src/window.c
+++ b/src/window.c
@@ -848,6 +848,12 @@ WWindow *wManageWindow(WScreen *scr, Window window)
 
 		/* // only enter here if PropGetWMClass() succeeds */
 		PropGetWMClass(wwin->main_window, &class, &instance);
+		if (!class || class[0] == '\0') {
+			if (wwin->wm_class && wwin->wm_class[0] != '\0')
+				class = strdup(wwin->wm_class);
+			else
+				class = strdup("default");
+		}
 		buffer = StrConcatDot(instance, class);
 
 		index = WMFindInArray(scr->fakeGroupLeaders, matchIdentifier, (void *)buffer);