diff --git a/server-ce/config/env.sh b/server-ce/config/env.sh
index 7c12b7aa30..4f962680b7 100644
--- a/server-ce/config/env.sh
+++ b/server-ce/config/env.sh
@@ -17,6 +17,6 @@ export WEB_API_HOST=127.0.0.1
 # we need to set the TEXLIVE_IMAGE_USER to www-data so that the
 # sandboxed compiles container can access the files 
 # created by the web container.
-if [ "$SANDBOXED_COMPILES_SIBLING_CONTAINERS" = "true" ]; then
+if [ "${SANDBOXED_COMPILES_SIBLING_CONTAINERS:-}" = "true" ]; then
   export TEXLIVE_IMAGE_USER=www-data
 fi
\ No newline at end of file