diff --git a/drivers/net/wireless/ath/debug.c b/drivers/net/wireless/ath/debug.c
index a9eb787..dacfb23 100644
--- a/drivers/net/wireless/ath/debug.c
+++ b/drivers/net/wireless/ath/debug.c
@@ -55,7 +55,7 @@
 	case NL80211_IFTYPE_P2P_GO:
 		return "P2P-GO";
 	default:
-		return NULL;
+		return "UNKNOWN";
 	}
 }
 EXPORT_SYMBOL(ath_opmode_to_string);