diff --git a/vpnsetup.sh b/vpnsetup.sh
index 5e3b24f..4ae281c 100755
--- a/vpnsetup.sh
+++ b/vpnsetup.sh
@@ -82,6 +82,12 @@ if [ -z "$VPN_IPSEC_PSK" ] || [ -z "$VPN_USER" ] || [ -z "$VPN_PASSWORD" ]; then
   exiterr "All VPN credentials must be specified. Edit the script and re-enter them."
 fi
 
+case "$VPN_IPSEC_PSK $VPN_USER $VPN_PASSWORD" in
+  *[\\\"\']*)
+    exiterr "VPN credentials must not contain any of these characters: \\ \" '"
+    ;;
+esac
+
 if [ "$(sed 's/\..*//' /etc/debian_version 2>/dev/null)" = "7" ]; then
 cat <<'EOF'
 IMPORTANT: Workaround required for Debian 7 (Wheezy).
diff --git a/vpnsetup_centos.sh b/vpnsetup_centos.sh
index 8e97b5f..e815da0 100755
--- a/vpnsetup_centos.sh
+++ b/vpnsetup_centos.sh
@@ -85,6 +85,12 @@ if [ -z "$VPN_IPSEC_PSK" ] || [ -z "$VPN_USER" ] || [ -z "$VPN_PASSWORD" ]; then
   exiterr "All VPN credentials must be specified. Edit the script and re-enter them."
 fi
 
+case "$VPN_IPSEC_PSK $VPN_USER $VPN_PASSWORD" in
+  *[\\\"\']*)
+    exiterr "VPN credentials must not contain any of these characters: \\ \" '"
+    ;;
+esac
+
 echo "VPN setup in progress... Please be patient."
 echo