diff --git a/armsrc/crapto1.h b/armsrc/crapto1.h
index 4d5fec0fa..54d66c28c 100644
--- a/armsrc/crapto1.h
+++ b/armsrc/crapto1.h
@@ -88,7 +88,7 @@ static inline int filter(uint32_t const x)
 	f |= 0x3c8b0 >> (x >>  8 & 0xf) &  4;
 	f |= 0x1e458 >> (x >> 12 & 0xf) &  2;
 	f |= 0x0d938 >> (x >> 16 & 0xf) &  1;
-	return BIT(0xEC57E80A, 0xf);
+	return BIT(0xEC57E80A, f);
 }
 #ifdef __cplusplus
 }