diff --git a/build.sh b/build.sh
index 4f7dca8..5a0aae3 100644
--- a/build.sh
+++ b/build.sh
@@ -13,6 +13,13 @@ AMD64="http://ftp.computerbase.de/2dcb2daff6a9e2bf9a8f6a6d867b5391/4e04afba/AiO-
 ICONFILE=${ICON##*/}
 X86FILE=${X86##*/}
 AMD64FILE=${AMD64##*/}
+
+        if [ -e /var/tmp/opsi/upload/$TYPE/${PN}_${VERSION}-${RELEASE}.opsi ]
+        then
+                echo "package ${PN}_${VERSION}-${RELEASE}.opsi already generated"
+                exit 1
+        fi
+
 OUT=$(mktemp -d /tmp/output.XXXXXXXXXX) || { echo "Failed to create temp dir"; exit 1; }
 mkdir $OUT/$PN
 cp -Rv OPSI CLIENT_DATA $OUT/$PN