diff --git a/src/bits.c b/src/bits.c
index d860461..6ec7efa 100644
--- a/src/bits.c
+++ b/src/bits.c
@@ -47,7 +47,7 @@ int main(int argc, char **argv)
 {
 	IGNORE(argc);
 
-	const char* mask = argv[1] && lcheck(strlen(argv[1]) > 1, "expected 2 character mask") ? argv[1] : "01";
+	const char* mask = argv[1] && lcheck(argv[1][0] && argv[1][1], "expected 2 character mask") ? argv[1] : "01";
 	unsigned char buf[BUFFER_SIZE];
 	char tbuf[BUFFER_SIZE * 8];
 	size_t bsz = BUFFER_SIZE;