diff --git a/arch/arm/lib/memset.S b/arch/arm/lib/memset.S
index 6ca4535c47fb63..e36d053a8a9030 100644
--- a/arch/arm/lib/memset.S
+++ b/arch/arm/lib/memset.S
@@ -16,6 +16,7 @@
 ENTRY(mmioset)
 ENTRY(memset)
 UNWIND( .fnstart         )
+	and	r1, r1, #255		@ cast to unsigned char
 	ands	r3, r0, #3		@ 1 unaligned?
 	mov	ip, r0			@ preserve r0 as return value
 	bne	6f			@ 1