diff --git a/pyshacl/errors.py b/pyshacl/errors.py
index 0e0a18e..e8e3f0b 100644
--- a/pyshacl/errors.py
+++ b/pyshacl/errors.py
@@ -2,7 +2,7 @@
 
 
 class ReportableRuntimeError(RuntimeError):
-    def __init__(self, message):
+    def __init__(self, message: str) -> None:
         self.message = message
 
     @property