diff --git a/deny.toml b/deny.toml
index 5f25788a..4e2681af 100644
--- a/deny.toml
+++ b/deny.toml
@@ -23,7 +23,7 @@ allow-osi-fsf-free = "either"
 confidence-threshold = 0.8
 
 [bans]
-multiple-versions = "warn"
+multiple-versions = "deny"
 highlight = "all"
 
 skip-tree = [