diff --git a/lib/arm-mes/arm.M1 b/lib/arm-mes/arm.M1
index 1182baf1..82ca0706 100644
--- a/lib/arm-mes/arm.M1
+++ b/lib/arm-mes/arm.M1
@@ -232,6 +232,7 @@ DEFINE sxtb__%r0,%r0 7000afe6
 DEFINE sxtb__%r1,%r1 7110afe6
 DEFINE sxth__%r0,%r0 7000bfe6
 DEFINE uxtb__%r0,%r0 7000efe6
+DEFINE uxtb__%r1,%r1 7110efe6
 DEFINE uxth__%r0,%r0 7000ffe6
 
 # deprecated, remove after 0.18