diff --git a/build.sh b/build.sh
index bafea79..7cffec2 100644
--- a/build.sh
+++ b/build.sh
@@ -11,11 +11,18 @@ AMD64="http://downloads.sourceforge.net/sevenzip/7z920-x64.msi"
 ICONFILE=${ICON##*/}
 X86FILE=${X86##*/}
 AMD64FILE=${AMD64##*/}
+
 OUT=$(mktemp -d /tmp/output.XXXXXXXXXX) || { echo "Failed to create temp dir"; exit 1; }
 mkdir $OUT/$PN
 cp -Rv OPSI CLIENT_DATA $OUT/$PN
 unix2dos $OUT/$PN/CLIENT_DATA/*
 
+	if [ -e /var/tmp/opsi/upload/$TYPE/${PN}_${VERSION}-${RELEASE}.opsi ]
+	then
+		echo "package ${PN}_${VERSION}-${RELEASE}.opsi already generated"
+		exit 1
+	fi
+
 	if [ -e /usr/portage/distfiles/$ICONFILE ]
 	then
 		if [ -e $ICONFILE.sha1sum ]