diff --git a/utils/casctl b/utils/casctl
index 8b94770..5912c6a 100755
--- a/utils/casctl
+++ b/utils/casctl
@@ -9,6 +9,9 @@ import sys
 import re
 import opencas
 
+if sys.version_info < (3, 5):
+    raise RuntimeError('At least Python 3.5 is required')
+
 def eprint(*args, **kwargs):
     print(*args, file=sys.stderr, **kwargs)