diff --git a/agents/plugins/mk_db2.aix b/agents/plugins/mk_db2.aix
index 4f8bf8f6223..08dbc731d64 100755
--- a/agents/plugins/mk_db2.aix
+++ b/agents/plugins/mk_db2.aix
@@ -1,4 +1,4 @@
-#!/usr/bin/ksh
+#!/usr/bin/ksh93
 # Copyright (C) 2019 Checkmk GmbH - License: GNU General Public License v2
 # This file is part of Checkmk (https://checkmk.com). It is subject to the terms and
 # conditions defined in the file COPYING, which is part of this source code package.
@@ -65,11 +65,11 @@ function waitmax {
 function query_instance {
     INSTANCE=$1
     # find home directory
-    HOMEDIR=$(grep "^$INSTANCE" /etc/passwd | awk -F: '{print $6}' | grep "$INSTANCE$")
+    HOMEDIR=$(grep -w "^$INSTANCE:" /etc/passwd | awk -F: '{print $6}')
     NOW=$(perl -e "print time();")
 
     waitmax 200 <<WAITMAX
-    su $INSTANCE << EOF
+    su - $INSTANCE -c "/usr/bin/ksh93" << EOF
 
     if [ ! -f $HOMEDIR/sqllib/db2profile ] ;
     then
@@ -99,7 +99,7 @@ function query_instance {
     DB_PORT='port 0'
     for DB in \\\$DBS; do
             db2 connect to \\\$DB > /dev/null;
-            if [ $? -nq 0 ] ; then
+            if [ $? -ne 0 ] ; then
                 exit 1
             fi