diff --git a/firmware/asm/arm/memset.S b/firmware/asm/arm/memset.S
index 682da874ce..64cd95cc9e 100644
--- a/firmware/asm/arm/memset.S
+++ b/firmware/asm/arm/memset.S
@@ -50,6 +50,7 @@ memset:
 /*
  * we know that the pointer in r0 is aligned to a word boundary.
  */
+        and     r1, r1, #255            @ clear sign bits
         orr     r1, r1, r1, lsl #8
         orr     r1, r1, r1, lsl #16
         mov     r3, r1