diff --git a/_constraints b/_constraints
index 770e5c8..fd79db7 100644
--- a/_constraints
+++ b/_constraints
@@ -6,7 +6,7 @@
     </conditions>
     <hardware>
       <cpu>
-        <flag>sse4.1</flag>
+        <flag>sse4_1</flag>
         <flag>avx</flag>
       </cpu>
     </hardware>