diff --git a/common/Makefile b/common/Makefile
index 564bc08a..e3d9e534 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -8,7 +8,8 @@ BASE          = $(TOP)/../common
 LOCALEDIR     = locale
 DOC_FILES     = $(wildcard $(LOCALEDIR)/*/*.xml)
 
-MAKE_JAR      = VERSION="$(VERSION)" DATE="$(BUILD_DATE)" sh $(BASE)/make_jar.sh
+export VERSION BUILD_DATE
+MAKE_JAR      = sh $(BASE)/make_jar.sh
 
 # TODO: specify source files manually?
 JAR_BASES     = $(TOP) $(BASE)
diff --git a/common/make_jar.sh b/common/make_jar.sh
index 8a5dfab9..97f4e194 100644
--- a/common/make_jar.sh
+++ b/common/make_jar.sh
@@ -52,6 +52,7 @@ do
     ) || exit 1
 done
 
-(cd $stage; zip -r "$top/$jar" *) || exit 1
+[ -f "$top/$jar" ] && rm -f "$top/$jar"
+(set -e; cd $stage; zip -r "$top/$jar" *) || exit 1
 rm -rf "$stage"