diff --git a/concrete_syntax/plantuml/renderer.py b/concrete_syntax/plantuml/renderer.py
index 0955a3c..9051fa2 100644
--- a/concrete_syntax/plantuml/renderer.py
+++ b/concrete_syntax/plantuml/renderer.py
@@ -28,7 +28,9 @@ def render_class_diagram(state, model, prefix_ids=""):
         if lower_card == None and upper_card == None:
             card_spec = ""
         else:
-            card_spec = f"{0 if lower_card == None else lower_card}..{"*" if upper_card == None else upper_card}"
+            low = "0" if lower_card == None else lower_card
+            upp = "*" if upper_card == None else upper_card
+            card_spec = f"{low}..{upp}"
 
         if is_abstract:
             output += f"\nabstract class \"{name} {card_spec}\" as {make_id(class_node)}"
diff --git a/framework/conformance.py b/framework/conformance.py
index b163040..e175e64 100644
--- a/framework/conformance.py
+++ b/framework/conformance.py
@@ -23,7 +23,8 @@ def render_conformance_check_result(error_list):
     if len(error_list) == 0:
         return "OK"
     else:
-        return f"There were {len(error_list)} errors: \n  {'\n  '.join(error_list)}"
+        joined = '\n  '.join(error_list)
+        return f"There were {len(error_list)} errors: \n  {joined}"
 
 
 class Conformance: