diff --git a/docker/test.yaml b/docker/test.yaml
index 27640b03..8bbb933c 100644
--- a/docker/test.yaml
+++ b/docker/test.yaml
@@ -14,17 +14,20 @@
 # ------------------------------------------------------------------------------
 version: "3.4"
 
+# Note that we do not need to specify PDO_HOSTNAME or PDO_LEDGER_URL
+# (or the corresponding --inteface or --ledger switches) for the test
+# scripts because they are hard coded in run_*_tests.sh for each of the
+# containers.
+
 services:
   ccf_container:
     environment:
       - PDO_VERSION=${PDO_VERSION}
-      - PDO_HOSTNAME=localhost
     entrypoint: /project/pdo/tools/run_ccf_tests.sh
 
   services_container:
     environment:
       - PDO_VERSION=${PDO_VERSION}
-      - PDO_HOSTNAME=localhost
       - PDO_LOG_LEVEL=${PDO_LOG_LEVEL:-info}
       - PDO_DEBUG_BUILD=${PDO_DEBUG_BUILD:-0}
     entrypoint: /project/pdo/tools/run_services_tests.sh
@@ -32,7 +35,6 @@ services:
   client_container:
     environment:
       - PDO_VERSION=${PDO_VERSION}
-      - PDO_HOSTNAME=localhost
       - PDO_LOG_LEVEL=${PDO_LOG_LEVEL:-info}
       - PDO_DEBUG_BUILD=${PDO_DEBUG_BUILD:-0}
     entrypoint: /project/pdo/tools/run_client_tests.sh