diff --git a/src/librustc_session/lint/builtin.rs b/src/librustc_session/lint/builtin.rs
index e55ddc26a9441..16771f70fe312 100644
--- a/src/librustc_session/lint/builtin.rs
+++ b/src/librustc_session/lint/builtin.rs
@@ -224,7 +224,7 @@ declare_lint! {
 
 declare_lint! {
     pub UNALIGNED_REFERENCES,
-    Allow,
+    Deny,
     "detects unaligned references to fields of packed structs",
 }