diff --git a/deployment.sh b/deployment.sh
index c6f7de6..da7fc17 100755
--- a/deployment.sh
+++ b/deployment.sh
@@ -313,11 +313,11 @@ if [ -n "$PROFILE" ] && [ -n "$NETSCRIPT_SERVER" ] ; then
 fi
 
 # check, if both SP/CE version and ngcp-installer version are present
-if [ $SP_VERSION && ! $INSTALLER_VERSION ] ; then
+if [ -n "$SP_VERSION" ] && [ -z "$INSTALLER_VERSION" ] ; then
   echo "Error: SP/CE version, but no ngcp-installer version specified" >&2
   exit 1
 fi
-if [ ! $SP_VERSION && $INSTALLER_VERSION ] ; then
+if [ -z $SP_VERSION ] && [ -n $INSTALLER_VERSION ] ; then
   echo "Error: ngcp-installer version, but no SP/CE version specified" >&2
   exit 1
 fi