diff --git a/PyKCS11/__init__.py b/PyKCS11/__init__.py
index 2e7499c..a3b6d75 100644
--- a/PyKCS11/__init__.py
+++ b/PyKCS11/__init__.py
@@ -474,6 +474,10 @@ def __del__(self):
             if not hasattr(self, "pkcs11dll_filename"):
                 return
 
+            # in case the load failed
+            if self.pkcs11dll_filename not in PyKCS11Lib._loaded_libs:
+                return
+
             # decrease user number
             PyKCS11Lib._loaded_libs[self.pkcs11dll_filename]["nb_users"] -= 1