diff --git a/contracts/ownership/Shareable.sol b/contracts/ownership/Shareable.sol
index 0cbf7d37d..8b8477d41 100644
--- a/contracts/ownership/Shareable.sol
+++ b/contracts/ownership/Shareable.sol
@@ -64,6 +64,9 @@ contract Shareable {
       ownerIndex[_owners[i]] = 2 + i;
     }
     required = _required;
+    if (required > owners.length) {
+      throw;
+    }
   }
 
   // Revokes a prior confirmation of the given operation