diff --git a/cmk/gui/plugins/webapi/webapi.py b/cmk/gui/plugins/webapi/webapi.py
index c0d9888216e11..0c6b119339578 100644
--- a/cmk/gui/plugins/webapi/webapi.py
+++ b/cmk/gui/plugins/webapi/webapi.py
@@ -41,6 +41,7 @@
 from cmk.gui.exceptions import MKUserError, MKAuthException, MKException
 from cmk.gui.plugins.userdb.htpasswd import hash_password
 import cmk.gui.watolib.users
+from cmk.gui.valuespec import Checkbox
 from cmk.gui.watolib.tags import (
     TagConfigFile,)
 from cmk.gui.watolib.groups import (
@@ -676,6 +677,11 @@ def _set(self, request):
         for folder_path, rules in new_ruleset.items():
             for rule in rules:
                 value = rule["value"]
+
+                # Binary rulesets currently don't have a valuespec attribute set.
+                if rule_vs is None:
+                    rule_vs = Checkbox()
+
                 try:
                     rule_vs.validate_datatype(value, "test_value")
                     rule_vs.validate_value(value, "test_value")