diff --git a/src/NoPELib/expansionsLib.py b/src/NoPELib/expansionsLib.py
index 186d938..2c6c16b 100644
--- a/src/NoPELib/expansionsLib.py
+++ b/src/NoPELib/expansionsLib.py
@@ -46,7 +46,7 @@ class Expansion:
         onError: 
     """
 
-    def __init__(self, ID: str, expansionsManager):
+    def __init__(self, ID: str, expansionsManager: "ExpansionsManager"):
         """
         Initialise the creation of an expansion and raise an error if not
         available.