diff --git a/lib/arm-mes/arm.M1 b/lib/arm-mes/arm.M1
index 71e55726..bae61169 100644
--- a/lib/arm-mes/arm.M1
+++ b/lib/arm-mes/arm.M1
@@ -179,6 +179,7 @@ DEFINE ldrsb__%r3,(%r3) d030d3e1  # ldrsb   r3, [r3]
 DEFINE ldrsb__%r4,(%r4) d040d4e1  # ldrsb   r4, [r4]
 DEFINE ldrsb__%r5,(%r5) d050d5e1  # ldrsb   r5, [r5]
 DEFINE strb___%r0,(%r0) 0000c0e5  # strb    r0, [r0]
+DEFINE strb___%r0,(%r1) 0000c1e5  # strb    r0, [r1]
 DEFINE strb___%r1,(%r1) 0010c1e5  # strb    r1, [r1]
 DEFINE strb___%r2,(%r2) 0020c2e5  # strb    r2, [r2]
 DEFINE strb___%r3,(%r3) 0030c3e5  # strb    r3, [r3]