diff --git a/tests/common.sh b/tests/common.sh
index 01090e97..fd50b82a 100644
--- a/tests/common.sh
+++ b/tests/common.sh
@@ -1,5 +1,5 @@
 [ -n "$VERBOSE" ] && set -x
-${ARENA:=test-arena}
+: ${ARENA:=test-arena}
 THISDIR=$(dirname $0)
 ARENA=${ARENA}/${THISDIR##*/}
 rm -rf $ARENA