diff --git a/test/README.md b/test/README.md
index 99e91bb8..9d7cbdc7 100644
--- a/test/README.md
+++ b/test/README.md
@@ -33,8 +33,8 @@ to run everything named `*_test.sh`.
 
 By default the tests assume the Vagrant VMs are used.
 
-To use other VMs, set the environment variables <var>HOST1</var> and
-<var>HOST2</var> to the IP addresses of two docker hosts, and set the
+To use other VMs, set the environment variable <var>HOSTS</var> to the
+space-separated list of IP addresses of the docker hosts, and set the
 environment variable <var>SSH</var> to a command that will log into
 either (which may just be `ssh`).
 
diff --git a/test/config.sh b/test/config.sh
index 7acba9ec..9bd15125 100644
--- a/test/config.sh
+++ b/test/config.sh
@@ -7,15 +7,16 @@ N_MACHINES=${N_MACHINES:-2}
 IP_PREFIX=${IP_PREFIX:-192.168.48}
 IP_SUFFIX_BASE=${IP_SUFFIX_BASE:-10}
 
-HOSTS=
-for i in $(seq 1 $N_MACHINES); do
-    IP="${IP_PREFIX}.$((${IP_SUFFIX_BASE}+$i))"
-    HOSTS="$HOSTS $IP"
-done
+if [ -z "$HOSTS" ] ; then
+    for i in $(seq 1 $N_MACHINES); do
+        IP="${IP_PREFIX}.$((${IP_SUFFIX_BASE}+$i))"
+        HOSTS="$HOSTS $IP"
+    done
+fi
 
 # these are used by the tests
-HOST1="${IP_PREFIX}.$((${IP_SUFFIX_BASE}+1))"
-HOST2="${IP_PREFIX}.$((${IP_SUFFIX_BASE}+2))"
+HOST1=$(echo $HOSTS | cut -f 1 -d ' ')
+HOST2=$(echo $HOSTS | cut -f 2 -d ' ')
 
 . ./assert.sh