diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6e5843e..89bbe8c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,8 @@ Note: Breaking changes between versions are indicated by "💥".
 
 ## Unreleased
 
+- [Bugfix] Fix (agin) forum starting issue: "NoMethodError: undefined method `encode' for nil:NilClass".
+
 ## v12.1.1 (2021-09-17)
 
 - [Bugfix] Fix forum starting issue: "NoMethodError: undefined method `encode' for nil:NilClass".
diff --git a/tutor/templates/build/forum/Dockerfile b/tutor/templates/build/forum/Dockerfile
index 2bb7c23..0bbbbd2 100644
--- a/tutor/templates/build/forum/Dockerfile
+++ b/tutor/templates/build/forum/Dockerfile
@@ -45,7 +45,7 @@ ENV NEW_RELIC_ENABLE false
 ENV API_KEY forumapikey
 ENV SEARCH_SERVER "http://elasticsearch:9200"
 ENV MONGODB_AUTH ""
-ENV MONGOID_AUTH_MECH ":scram"
+ENV MONGOID_AUTH_MECH ""
 ENV MONGODB_HOST "mongodb"
 ENV MONGODB_PORT "27017"
 ENV MONGODB_DATABASE "cs_comments_service"
diff --git a/tutor/templates/build/forum/bin/docker-entrypoint.sh b/tutor/templates/build/forum/bin/docker-entrypoint.sh
index 77cd2b0..4f5ac7c 100755
--- a/tutor/templates/build/forum/bin/docker-entrypoint.sh
+++ b/tutor/templates/build/forum/bin/docker-entrypoint.sh
@@ -4,6 +4,12 @@ export MONGOHQ_URL="mongodb://$MONGODB_AUTH$MONGODB_HOST:$MONGODB_PORT/$MONGODB_
 # the search server variable was renamed after the upgrade to elasticsearch 7
 export SEARCH_SERVER_ES7="$SEARCH_SERVER"
 
+# make sure that there is an actual authentication mechanism in place, if necessary
+if [ -n "$MONGODB_AUTH" ]
+then
+    export MONGOID_AUTH_MECH=":scram"
+fi
+
 echo "Waiting for mongodb/elasticsearch..."
 dockerize -wait tcp://$MONGODB_HOST:$MONGODB_PORT -wait $SEARCH_SERVER -wait-retry-interval 5s -timeout 600s