diff --git a/libs/openzap/src/isdn/Q921.c b/libs/openzap/src/isdn/Q921.c
index a682c2342e..2c7c740251 100644
--- a/libs/openzap/src/isdn/Q921.c
+++ b/libs/openzap/src/isdn/Q921.c
@@ -817,6 +817,8 @@ static int Q921LogMesg(L2TRUNK trunk, Q921LogLevel_t level, L2UCHAR received, L2
 	}
 
 out:
+	buf[sizeof(buf) - 1] = '\0';
+
 	return trunk->Q921LogProc(trunk->PrivateDataLog, level, buf, strlen(buf));
 }