diff --git a/package.sh b/package.sh
index b9602a4..99c38a8 100755
--- a/package.sh
+++ b/package.sh
@@ -1,23 +1,31 @@
-#!/bin/bash
+#!/bin/bash -e
 
 VER=$1
-
 if [ -z $1 ]; then
-  echo version must be specified: x.y.z
+  echo target PGXN package version must be specified: x.y.z
   exit;
 fi
 
+TAG=$2
+if [ -z $2 ]; then
+  echo datasketches-postgresql git tag must be specified
+  exit;
+fi
+
+# version of datasketches-cpp core library to include
+CORETAG=1.0.0-incubating
+
 DST=datasketches-$VER
 
 PGARCH=postgresql-$VER.zip
-COREARCH=core-$VER.zip
+COREARCH=core-$CORETAG.zip
 
 rm -rf $DST
-rm $DST.zip
+rm -f $DST.zip
 
-git archive --format zip --prefix=$DST/ --output $PGARCH master
+git archive --format zip --prefix=$DST/ --output $PGARCH $TAG
 cd ../datasketches-cpp
-git archive --format zip --output ../datasketches-postgresql/$COREARCH master
+git archive --format zip --output ../datasketches-postgresql/$COREARCH $CORETAG
 cd ../datasketches-postgresql
 
 unzip $PGARCH