diff --git a/src/pcd.rs b/src/pcd.rs
index 2277851..a5247d8 100644
--- a/src/pcd.rs
+++ b/src/pcd.rs
@@ -324,6 +324,8 @@ impl ValidationRule {
             return Err(Error::msg("Field isn't part of this rule"));
         } else if members.is_empty() {
             return Err(Error::msg("Members list is empty"));
+        } else if self.quorum <= 0.0 || self.quorum > 1.0 || self.quorum.is_sign_negative() || self.quorum.is_nan() { // Just to be sure
+            return Err(Error::msg("This rule is read only"));
         }
 
         let required_members = (members.len() as f32 * self.quorum).ceil() as usize;