diff --git a/openbsc/src/gprs/gprs_gmm.c b/openbsc/src/gprs/gprs_gmm.c
index 68ba326..5848a63 100644
--- a/openbsc/src/gprs/gprs_gmm.c
+++ b/openbsc/src/gprs/gprs_gmm.c
@@ -1464,7 +1464,10 @@
 	default:
 		LOGMMCTXP(LOGL_NOTICE, mmctx, "Unknown GSM 04.08 GMM msg type 0x%02x\n",
 			gh->msg_type);
-		rc = gsm48_tx_gmm_status(mmctx, GMM_CAUSE_MSGT_NOTEXIST_NOTIMPL);
+		if (mmctx)
+			rc = gsm48_tx_gmm_status(mmctx, GMM_CAUSE_MSGT_NOTEXIST_NOTIMPL);
+		else
+			rc = -EINVAL;
 		break;
 	}