diff --git a/src/bits.c b/src/bits.c
index 6b7a351..c1f698b 100644
--- a/src/bits.c
+++ b/src/bits.c
@@ -55,7 +55,12 @@ int main(int argc, char **argv)
 {
 	IGNORE(argc);
 
-	const char* mask = argv[1] && Lcheck(argv[1][0] && argv[1][1], "expected 2 character mask") ? argv[1] : "01";
+	const char* mask = argv[1] && 
+				Lcheck( argv[1][0] && // We only care about the first 2 chars, so check them both. If neither are the null terminator, then the mask is valid. 
+					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;