diff --git a/cwltool.Dockerfile b/cwltool.Dockerfile
index 4fa76b126..2b93b8d99 100644
--- a/cwltool.Dockerfile
+++ b/cwltool.Dockerfile
@@ -4,7 +4,7 @@ RUN apk add --no-cache git gcc python3-dev libxml2-dev libxslt-dev libc-dev linu
 
 WORKDIR /cwltool
 COPY . .
-RUN export SETUPTOOLS_SCM_PRETEND_VERSION_FOR_CWLTOOL=$(grep __version__ cwltool/_version.py  | awk -F\' '{ print $2 }') ; \
+RUN export SETUPTOOLS_SCM_PRETEND_VERSION_FOR_CWLTOOL=$(grep __version__ cwltool/_version.py  | awk -F\' '{ print $2 }' | tr -d '\\n') ; \
 	CWLTOOL_USE_MYPYC=1 MYPYPATH=mypy-stubs pip wheel --no-binary schema-salad \
 	--wheel-dir=/wheels .[deps]  # --verbose
 RUN rm /wheels/schema_salad*
diff --git a/cwltool/software_requirements.py b/cwltool/software_requirements.py
index 9360e8080..ec99bda05 100644
--- a/cwltool/software_requirements.py
+++ b/cwltool/software_requirements.py
@@ -159,7 +159,7 @@ def get_container_from_software_requirements(
             [DOCKER_CONTAINER_TYPE], tool_info
         )
         if container_description:
-            return container_description.identifier
+            return str(container_description.identifier)
 
     return None