diff --git a/scripts/mbedtls_dev/crypto_knowledge.py b/scripts/mbedtls_dev/crypto_knowledge.py
index c38955b..6b38aac 100644
--- a/scripts/mbedtls_dev/crypto_knowledge.py
+++ b/scripts/mbedtls_dev/crypto_knowledge.py
@@ -26,7 +26,7 @@
 class KeyType:
     """Knowledge about a PSA key type."""
 
-    def __init__(self, name: str, params: Optional[Iterable[str]] = None):
+    def __init__(self, name: str, params: Optional[Iterable[str]] = None) -> None:
         """Analyze a key type.
 
         The key type must be specified in PSA syntax. In its simplest form,