diff --git a/_dockerfile_shell.sh b/_dockerfile_shell.sh
index 860209e..92125c0 100755
--- a/_dockerfile_shell.sh
+++ b/_dockerfile_shell.sh
@@ -7,4 +7,9 @@ if [[ "${MAMBA_DOCKERFILE_ACTIVATE}" == "1" ]]; then
   source _activate_current_env.sh
 fi
 
+# Set umask if given
+if [[ ! -z "${DOCKERFILE_UMASK}" ]]; then
+  umask "${DOCKERFILE_UMASK}"
+fi
+
 exec bash -o pipefail -c "$@"