diff --git a/myst_libre/builders/myst_builder.py b/myst_libre/builders/myst_builder.py
index 4082d6f..d50504d 100644
--- a/myst_libre/builders/myst_builder.py
+++ b/myst_libre/builders/myst_builder.py
@@ -14,6 +14,9 @@ def __init__(self, hub):
                          "port":f"{self.hub.port}"
                          }
         self.myst_client = MystMD(hub.rees.build_dir, self.env_vars)
+    
+    def setenv(self,key,value):
+        self.env_vars[key] = value
 
     def build(self):
         self.cprint(f'Starting MyST build {self.hub.jh_url}','yellow')
diff --git a/myst_libre/tools/jupyter_hub_local_spawner.py b/myst_libre/tools/jupyter_hub_local_spawner.py
index 95d4847..08ddbb6 100644
--- a/myst_libre/tools/jupyter_hub_local_spawner.py
+++ b/myst_libre/tools/jupyter_hub_local_spawner.py
@@ -78,9 +78,9 @@ def spawn_jupyter_hub(self):
         self.jh_token = h.hexdigest()
 
         if not self.rees.search_img_by_repo_name():
-            raise Exception(f"[ERROR] A docker image has not been found for {self.rees.gh_user_repo_name} at {self.binder_image_tag}.")
+            raise Exception(f"[ERROR] A docker image has not been found for {self.rees.gh_user_repo_name} at {self.rees.binder_image_tag}.")
         if self.rees.binder_image_tag not in self.rees.found_image_tags:
-            raise Exception(f"[ERROR] A docker image exists for {self.rees.gh_user_repo_name}, yet the tag {self.binder_image_tag} is missing.")
+            raise Exception(f"[ERROR] A docker image exists for {self.rees.gh_user_repo_name}, yet the tag {self.rees.binder_image_tag} is missing.")
         
         # self.rees.found_image_name is assigned if above not fails